I actually run the testing repo from Arch, and have been for the last 6 months. Quite stable actually, no hiccups I can remember (I don't really recommend it though, unless you can either fix the problems or plan on reporting bugs).
But yeah, update OFTEN.
Second piece of advice, when doing updates, take note of what's updating. Especially the stuff that you use often. I'm always wary of updating MySQL or Awesome WM, due to potential breakages (which is fine, but I don't always have the time to fix them before using them).
Oh, and if you find that a package doesn't exist in the Arch repos, check AUR (using something like yaourt). Chances are, it'll be there.
Probably the main feature (other than pacman, and the build up philosophy) that keeps me with Arch Linux.