Stick with AS1&2 or switch AS3?

Im going to be relearning Flash soon, last version I used was FlashMX and I believe it was AS1 (although AS2 wasnt a huge leap of difference and i had dabbled with it)

All my old work (of which theres a fair bit) is in AS1 or AS2.
Im aware (correct me if im wrong) that Flash CS4 allows the use of AS2 still, so basically is it worthwhile me actually learning AS3, what are its advantages from a web design point of view.
From what ive read it seems more useful for flash games and the like but im not convinced its going to be worth the huge effort to learn AS3, as it will be like starting again (in a sense)

So what do you guys think?
Bearing in mind this is purely for web page development, is AS3 worth the hassle?
Or is it better to learn AS3 now and save myself the trouble later before i pick up all those old AS1&2 habits again?