I wouldn't say I unlearned. I think it's more like mixing up different languages, if we like it or not (using Perl logics in Cobol code is just plain wicked :)) ). I actively program in 2 other languages besides Perl (most other languages I learned once are still in my memory somewhere, somehow). If you don't practise something (anything!), you loose your touch. It's all about setting priorities :)

Greetz
Beatnik
... Quidquid perl dictum sit, altum viditur.