So I bought a used mtb for a commuter a few months back. I'd noticed the cassette had a wobble to it, but it worked, so I put off dealing with it. Well, I got around to repacking the bearings this weekend, and when I pulled out the axle - well it came out in 2 pieces! Mystery of the wobble solved. A quick trip to the LBS, and I replaced that axle, repacked everything.

This morning, no wobble on my commute, temps in the low 60s, sunny, it was pretty sweet!