I experienced several times that I automatically didn't think in German but in English. I just remember one first day of the semester, I was going to uni to a lecture of Italian and I thought in English what I have to buy after the lectures in the grocery store.
I guess it would get to a point in one's mastery of a language that it becomes natural to think with it, occasionally.
it happens..at me when i write a lot here or in msn (in english)...
Of course, I was merely commenting how strange it would be for myself. I'm talentless when it comes to linguistic ability.
To me it happens all the time especially when I'm in Argentina.
Which languages are you proficient in?