The iBook G4 has improved "a lot" over the previous generation
No, I can't tell you any issue after a week using my brand new iBook G4 800MHz. The machine runs OS X 10.3.3 (very smoothly BTW) and I definitely recommend it. I've upgraded the RAM to 640MB tough, but I didn't notice "that" difference after the upgrade, only in specific apps like VPC. These iBook feels very fast (even with 256MB) if compared to my previous iBook G3 600MHz. I mean, the gap is huge. Maybe it's Panther, maybe not. But it does feel a lot faster. And the battery is amazing, pretty easy to get 5 hours doing "soft" stuff, like web surfing, reading and creating documents with the screen dimmed to 50%. You can get better marks actually, if you want to.