Yeah, some additional memory will help having a few apps open, or complicated web pages etc. but as for YouTube, forget it. Even my G4 1.33GHz won't play YouTube videos properly due to the flash plugin not really using the hardware properly. Which is a shame, seeing as I use it for editing full-screen (non-HD) video via firewire with no problems whatsoever.
I've come across that battery problem in some iBooks too - guess I'm just very lucky with mine. Most laptops will start showing battery issues after a few years, Apple are no exception.
