Hi Russ, I have the Skytracker, and I can give you a little information that might help your decision (I posted it first on
Shelley's Polarie thread):
I've been using the Skytracker for a few months now, and having a lot of fun with it. If you want, you can look at my photo albums via my sig to see what I've managed with it - imaging Pluto at 250mm, or some decent deep sky 100mm and 250mm shots are possible (with stars detected to 17th/18th mag at a dark site). The polar scope is a massive plus with the Skytracker - my set-up time is minimal (5-10mins max) with the polar scope and "Polar Finder" app, and then the alignment errors are much less (negligible, really) than the periodic error in the drive. Azimuth alignment is more fiddly on the Skytracker than altitude but my tripod compensates for that.
I've measured my PE at 48", in a roughly sinusoidal peak-to-peak, with 2-3minute stationary points on either side of the oscillation. For exposure times, at the moment I'm limited to 2-minute exposures @250mm (EOS 60D), and I'll reject >50% of those shots due to PE trailing. At 100mm with 3-minute exposures, I'll reject <33% of frames due to PE. I don't reject many frames at all for polar alignment errors. So periodic error will severely limit you on focal lengths much bigger than 250mm with the Skytracker, unless you're lucky and get a much better one than mine. The weight of a really big lens might also be too much?