Well, it doesn't actually do the updating for you, just alerts the new version's existence and downloads it from my site. But it does mean users don't have to check the forum for newer versions.
It's not overly complicated; I wrote it up a couple years back:
I do use two servers to try to add some file integrity protection: The downloads come from my server, but then they're verified using SHASUM values downloaded from a different server. I've been pretty happy with how well it's worked for me.
-rob.