The Team does have a few instructions, though, for the folks that updated. So if you have installed Mountain Lion, and you plan on using the utility, you should read this…
From The Dev Team blog:
“Update #1 7/25/12: redsn0w is compatible with today’s retail release of Mountain Lion OS X 10.8. Until we start using an official developer ID for it (!), you’ll need to use the new Ctrl-Click-Open security bypass the first time you run it after downloading.”
Other than that, you shouldn’t have any problems with RedSn0w in OS X 10.8.