I switch quite often. Sometimes 3 languages a day: Delphi/Lazarus/FreePascal, C++ and Javascript so it now takes few minutes to adjust.

I try not to switch too often, just because I find it hard to remember the details. The one that always stumps me the most is comments -- I always stare for several seconds trying to remember how comments work in that language.

Oh, I completely agree. I do not switch because I want to, but because I have to.