In my experience (including typing this on my PowerBook5,8 running 10A96), not really, no. Mind you, this is after applying many of the fixes and component swaps with the later 10.5.8 counterparts.
Running QuickTime 7.7.0 for Leopard, I can view SD mp4 video. FPS varies usually between 18 and 24fps, which obviously isn’t perfect, but considering the CPU is handling the playback, it’s better than expected. VLC is a no-go for video (because it’s looking for that GPU and can’t engage it). And I’ve never been a gamer, so graphics-intensive stuff, like vector drawing and refresh, probably isn’t what you might expect if running Leopard.
Otherwise, however? There are still a couple of predictable quirks endemic of a work-in-progress system, but it’s remarkably solid and good enough that, even though this PowerBook is split into two partitions (10A96 and 10.5.8), I’ve virtually never used 10.5.8 on it (unless it’s to log in as root so I can swap system-level components in 10A96 for testing). I find using InterwebPPC to be a pretty smooth experience overall, and the UI is pretty decent, as well.