As with virtually all Apple software, Motion is designed to sell boxes. Not software boxes, CPU boxes. In fact, I can think of no other app in Apple history that is so specifically designed to move high end G5s.
I also bought Motion, but I knew full well it wasn't going to work on any of my machines. It'll just be a nice bonus when I get a G5 soon-ish, maybe.
Rant alert:
Saw a horrible Motion demo at the Chicago Apple store. The presenter (Richard Harrington I think) was bloody awful. Out of one hour, the first ten minutes were burned just starting late for no apparent reason. The next ten minutes were burned talking about himself and polling the audience to see who used FCP, After Effects, etc. Here's a clue, nobody gives a crap. Just show us the freaking demo. Frankly, I learned WAY more just viewing the videos on Apple's site. The only reason I went was to get my name in the drawing for a G5. If I don't win (ha ha), I'd call it a total bust.
Here's another tidbit of advice. Apple isn't kidding when they talk about recommending 4 gig ram, a monster video card and a dual G5. The demo was on a dual 2 GHZ with I think 1 GIG RAM, but crippled by a 32 MB video card. Don't ask me why they couldn't have thrown in a better card for the demo. Anyway, Motion pretty much blows using those specs since the video card boittle-necks it. I got the impression that Motion simply expects the absolute top of the line machine to even begin delivering on its Real Time promise consistently. Note I said consistently. For some things, lesser machines will pull it off, but in general expect to hit a render [or slow frame rate] wall quickly in many cases.
But then, this is 1.0. And without a full implementation of CoreVideo. And machines only get better. Motion in a few years will be insane. For now, it's just wicked cool.