The site in my sig runs X Power and I love it. Took me a while to set up since there are so many features, but that's not a bad thing!
Accelman handles all the support and he's online on ICQ most of the time, and I'd be happy to answer any questions I can. Essentially the use of mod_rewrite allows all the PHP generated pages to have standard static URLs for spider friendliness. My site's still new and I'm getting some good crawls already. If you ever decide to go with it PM me or hit me up on ICQ and I can give you a few new user tips.