I took a course at PCMI some years ago from David Perkinson (Reed College). He did an amazing job and single-handedly convinced me it was possible to teach well from slides. Check out this link to see examples of his slides. As the other answers have mentioned, it seems necessary to use slides only in conjunction with the board. Perkinson did this, but also included a useful trick: he created handouts from the slides for students to write on, but left blank spots in those handouts so they had to write the proofs themselves based on what he said, showed on the slides, and wrote on the board.

Professor Perkinson is also a wizard of sorts with mathematica, and he was able to create awesome graphics using it. I don't think his mathematica code is online, but I'll bet he'd be willing to share if someone emailed him. He may also have tricks to reduce prep time, as this was the sort of thing he liked thinking about.