This seems like a good opportunity to write about my tests today.
I took an initial 5.2 miles ride with absolutely no hiccups. This ride included a couple patches of rough road and a hop over a curb. Also worth mention, the rig doesn't really create any drag. At least non taht I could feel. Want some numbers to back it up? I usually ride this route at a clip of 15.67mph. I averaged 16.45mph with the rig.

The second ride was more of a test. It was a 10.2 mile jaunt that took the the rig and I over several patches of rough road, fast downhills and a few long uphill climbs. Again, the rack performed flawlessly.
No squeaks, no signs of fractures or weakness, not even a shift of the milk box. Everything worked great.

Also, the zip-ties that were used to hold the frame of the rack against the back of the bike showed no sign of strain. I couldn't even force the things to stretch.