I've never used any of the wake-up features in either MP or Myth, mostly because my HTPC does other things (e.g. music, web server) and never really has much time to sleep. Still, what distro were you using? I'd be glad to help you if that was the only feature holding you back from trying out Myth again.
I've just gotten Ubuntu 6.10 downloaded, so when I get time I'll try that out - maybe they've gotten this built into the repo package.
I had to hack together an installation for myth 0.19 because when I was doing it on my Ubuntu 6.06 installation, it didn't have myth 0.19 in its repos.
Sam