Will there be full hardware-acceleration of the graphical effects, like Compiz provides,
Yes. There already is, in fact. Aaron Seigo has prepared a screencast which will be linked with this week's Commit Digest. Among other things, it shows the true transparency of Plasma applets and the panel. Also, you can check out these old (non-Plasma related) kwin_composite videos: http://www.youtube.com/watch?v=4WBLlc6xCQ4
or will KDE 4 continue to have ugly faux transparency?
Eavesdropping on IRC, I get the feeling that aseigo hates this hack more than you do