Right now, I am using the open source wyUpdate at work, along with wyBuild ($69). The experience has been marginal at best. No huge issues have arisen, and I love the binary patching and automatic patch creation, but wyBuild isn't updated nearly often enough and has a few prominent issues. My biggest problem with this software is that the file locations for building updates are stored with absolute paths. Additionally, the update checking fails on my development machine for no apparent reason, which is worrisome.
Some other options I have looked into (briefly) are dotnetautoupdate and Sparkle. A couple I haven't looked into are Sharp Autoupdater, and NAppUpdate.
Has anyone used an autoupdater before? What did you use, and how was your experience?