Disclaimer: Strictly speaking, I am not a native speaker of English. For most purposes, however, it is my best language. It would make little sense for me to list Portuguese as 5 if my English were listed as 4. I would like a more objective way of rating one's language skills, such as Cloze tests. Also, my Dutch should be a 3.5. See below for details.

Just give me a number!

Now, pending that, for the sake of projecting my language skills into a 1-dimensional axis, this is how I rate myself currently (15 March 2009) (5.0 is perfect fluency, 3.0 is bare fluency, and 0 is perfect ignorance. If I list a perfectly foreign language as 1.0, this means I've only spent 1/3 of the effort/time it takes to be barely fluent. e.g. Finnish is "perfectly foreign" and I listed it as 0.4 because I think I've only done ~13% of the work I would need to become barely fluent; my Italian is 2.0 even though I've done almost no work because it's not very foreign to me... I think it would take ~20 times as much effort for me to become fluent in Finnish than in Italian.):

English 4.9
Portuguese 4.8
Dutch 4.0 (moderate English influence)
French 3.5 (moderate Portuguese influence)
Spanish 3.2 (strong Portuguese influence; mostly broken, yet fairly fluent)
Catalan 2.8 (passive; understand it due to Portuguese, Spanish, French)
German 2.6 (strong Dutch influence; moderately broken)
Italian 2.0 (strong Portuguese, French influence; mostly broken)

For the languages below, any conversation is typically too hard to be worth the effort:

Nordic 1.0 (almost entirely due to English/Dutch/German)
Finnish 0.4
Russian 0.1
Mandarin 0.1
Japanese 0.1

More detail

Portuguese

My native dialect is from Recife, which is somewhat exceptional, even among Northeastern Brazilian dialects (henceforth "NE dialects"). My Recife dialect is characterized by:

lack of affrication, like most NE dialects ("tia" is pronounced [tía] rather than [tSía]).
pervasive fronting, like most NE dialects: "bonito" [bunítu], "escola" [iSkola], "menino" [minínu], "pendurar" [pindurá]. Even "peru" is pronounced [piru] by some people.
"e" often pronounced as [E], like most NE dialects. One exception is the verb "fechar", which exhibits the opposite pattern.
"s" becomes palatalized to [S] or [3] when immediately before a consonant, like in the Rio dialect (e.g. "casca" [kaSka] and "costa" [koSta]. In most NE dialects, this only occurs if the next letter is "t", so they say [kaska] but [koSta].
lack of pronoun in personal names, like most NE dialects ("Gustavo" rather than "o Gustavo")
singing intonation
"r" is [h] when doubled or when beginning a word, as in most of Brazil (but not much of Minas, São Paulo and the South).
extensive use of the diminutive
in sloppy language, replacing all kinds of fricatives by [h], "eu vou-me embora" [euhómimbóra] or [euhombóra]; "a gente" [ahénti]

In my definition, the Salvador dialect does not qualify as a NE dialect.

The Recife dialect is pretty conservative. Brazilians from other dialect regions often ask if from I'm from Portugal (my brother is often asked the same thing in São Paulo). I'm curious about the origins of Northeastern Brazilian dialects.

Over time, my Portuguese has deteriorated. But most of the time, people don't see anything wrong with it. Occasionally they may think I talk a bit weird.

English

I lived in London 1994-1997 and went to an International School. I had a mostly English accent, but never passed as a native speaker. In 1997, I went to college in the USA. I think it was around 1999 when someone really thought I was from the USA, and found it weird that I asked the question.

As for now (Dec 2008), I mostly pass for a native speaker (US/Canada dialect). Definitely not always, I suspect my word choice gives it away. But nobody guesses that I speak Portuguese. I'm not very good at naming animals, vegetables, cartoon characters: that's the price of growing up without English. (OTOH, even in Portuguse, I have trouble with "jacaré" vs "crocodilo", "sapo" vs "rã", etc.. I'm lacking a conceptual distinction, not just a lexical distinction).

Around 2000, I once was recognized as non-native because of my intonation.

In 2003, I moved to Amsterdam, and my classmates were mostly European. I had a girlfriend from Northern England, and did comedy improv with several British folks. Around 2004, I was told I had a mid-Atlantic accent. When I visited Pittsburgh in 2006, American accents sounded somewhat foreign, like a parody of themselves.

In 2006, my English reportedly had a Dutch accent. After a few months in Pittsburgh, I sounded American again (except for the occasional subtle thing).

In 2010, I moved from Vancouver to NYC. There's something I find very natural about the NYC accent, namely the non-rhotic "r" and perhaps the intonation. I'm sure it has affected my speech, but it's unclear how much this is perceptible to others.

Dutch

Dutch was fun. Difficult at first, of course. But most difficulties were rather superficial. I found it hard to not associate "-s" with plural, in adjectives/adverbs like "netjes" and "eventjes" (English has similar adverbial use of "-s", e.g. "unawares"). Also, the word order can be rather demanding: even now I'm uncomfortable with constructions like:

"de trambestuurder zag er de lol al lang niet meer van in" ("the tram driver saw there the fun already long not more of in", i.e. "the tram driver really didn't see the fun of it anymore (for long time)")
"Ik heb hem kunnen laten zien", i.e. "I was able to show him".

I understood the TV after about 3 months (I remember seeing the news that Saddam Hussein was caught on Dutch TV). After a year, several people took me for a native speaker, at least for the first few sentences. By the end of 2005, I could have reasonably long conversations without people suspecting I wasn't a native speaker. This is remarkable because, phonetically speaking, no other language has been this easy for me to sound like a native. Several Dutch people say that I speak "accentloos ABN".

See my page about Dutch.

German

90% of my German knowledge is borrowed from Dutch. During my first month in Munich, I had a constant smile on my face.

While I believe I can say all German phonemes, and maybe all phonemic distinctions, I still can't say "Feldkirchen" (the suburb where I worked) with the right intonation.

I miss the prefix "irgend-" in my other languages. e.g. in English, I want to say "somewhen" ("at some point"); in Dutch I often want to say something like "irgendwie" for "somebody" (the correct word is "iemand"). Confusingly "wie" means "who" in Dutch and "how" in German. In Portuguese I don't even search for the morpheme, since its morphological poverty is so obvious.

French

I studied a year or so in high school, and did 1 course + conversation classes in college. Last time I checked, when I asked, French speakers tended identify me as Spanish or Portuguese.

Spanish

Spanish speakers who have known Portuguese speakers can usually recognize me as one. Sometimes they can even tell specifically that I'm from Brazil.

See http://www.optimizelife.com/wiki/Public/Spanish

Italian

I really don't speak Italian worth a damn. But strangely enough, Italy is so rich in dialects that native speakers may not recognize me as foreign rightaway... I may have to say a couple of sentences before they notice that my words are all wrong.

Finnish

Being a language geek, I dedicated some time to learning a bit of Finnish on the Internet. I get a kick out of reading Finnish and surprising myself with my understanding. I have succeeded in having 5-line conversations, with much effort. 3 weeks in Helsinki taught me a lot! I estimate that my passive vocabulary peaked around 400 words.

Although it is very easy in terms of phonetics and spelling, it has by far the hardest grammar of any language I've ever played with. It feels like some words contain 3 or 4 suffixes, and the suffixes all modify each other.

Mandarin

I'm beginning to study spoken Mandarin (Pinyin), but after 3 lessons, it's not flowing yet.