Let me somewhat echo the above. I've got six months and near enough to 1200 miles as not to worry about it on my Topeak Explorer and some cheap 'house brand' type panniers. Both seem to be holding up just fine, though I've chosen to replace the hooks on my panniers with some much nicer (and heavier) items from Jandd Mountaineering. This was not strictly necessary, as 3 of the 4 hooks were in fine shape (the 4th, however, had gone AWOL while riding on the rutted, rocky towpath, and my homemade replacement wasn't really cutting it. I replaced the hooks and the hardware with some more secure stuff while I was at it). I look at Ortliebs and regret not getting a pair when I saw them on clearance at Best Buy many months ago.

I ride a Kona Dew Drop and had no trouble mounting the Topeak. I also have/had other racks on a couple of my other bikes, and similarly had no issues, so I believe the hardware is fairly standardized, in terms of nuts and bolts. Obviously, frame geometry affects fit, so there is definitely some playing required to get things fitted to your specific frame, which means bending the bracket-things on the low/middle end racks. Tubus has a different system that looks fabulous, though I've not tried it.

If you have the cash, and want to put it to the good stuff, then by all means get the Tubus and the Ortliebs. I'm confident you won't regret it.