About the soundcard thing, I've found that using my Audigy 2 ZS vs. my Soundstorm onboard sound only yields a frame or two at most, and in some cases can actually reduce framerates. EAX 3 certainly sounds better than the onboard when it works, but a lot of games don't support it properly, and I have yet to hear a game that actually sounded convincing (DOOM 3 is the best I've heard, and that uses its own sound mixing engine). I think a lot of work could be done on accelerated sound, but with jokers like Creative leading the industry, we're not going to get there for a while.
As for the PPU, I have mixed feelings about it. It sounds like a good idea in theory, but I'm a little leery of anything that's going to raise the entry bar for PC gaming even higher. Sure, I have a decent rig, but a lot of my buddies (with whom I play network games occasionally) have dinky budget video cards, even if their PC is relatively new. If a game needs a PPU card to perform acceptably, it's going to be difficult to get people who aren't hardcore gamers to play it. However, if general tasks can be offloaded to the card (for example, let's say I'm encoding a divx, I offload that task to the card so that my main CPU is still not bogged down), that would definitely help sell them.
Also, if these are on a seperate card (as opposed to being part of the graphics card), is PCI going to have sufficient bandwidth to make them useful? Or is this going to be a PCI-express only thing?
One more thing - heat and power consumption. If this thing can't run without a fan and without drawing additional power (ie having to hook it up directly to the PS), I'm not interested, and I imagine a lot of people probably feel the same way.