I know it's stupid but I don't put on my harness till I get to the top... It's so slow and the noise lasts so much longer if I take the time to move the harness up the tree as I go [:@]
One time as I was going up my climber (2 point system) hit a lump in the tree and slipped off. I was left dangline with the top portion of my climber under my armpits. Luckily it wasn't just my hands on my climber or I would have been gone! After regaining my composure I remembered that my lower end was tied onto the top end and it was just high enough that I could snag it with my foot and bring it up.

It's happened to me a few times worse than that but luckily it was while I had a buddy or two right below me...