[Michel_80]

Is there somewhere a list of all altivec apps? I am trying to decide whether I am going to use them or not, which will determine whether to buy an Ibook or a Powerbook?

[Evinyatar]

I'm not aware of an actual list, but most CPU intensive commercial applications are AltiVec optimized (Photoshop, Cinema 4D, Maya, Final Cut Pro, the 3ivx codec, ...) and several free ones too (QuickTime, iTunes, ...).
Plus huge parts of MacOS X are AltiVec optimized as well (Quartz being the most important one here I think) which will improve the speed on all applications, regardless of wether they are optimized themselves.

And you'll also get a faster graphics card in the PowerBook