An early warning: Brewfest has definitely been updated for Mists of Pandaria. We don't have solid information on all of the changes yet, but in the hours after the holiday goes live, I'll be around to make sure that everything in the guide is updated and corrected for the new expansion.
This year, Brewfest runs from Friday, Sept. 28 to Sunday, Oct. 14 (check your in-game calendar for your server's exact start and end times: Different time zones mean your Brewfest may end late on Saturday, Oct. 13). Why so late and so long this year? Because Coren Direbrew's been jacked to level 90, and you can't queue for him until level 89 at the earliest. Blizzard's planned around the awkwardness of having Brewfest go live so close to the Mists launch by bumping the holiday back by a week and extending the amount of time you'll have to get everything done if you're starting from scratch.
So don't worry about leveling at a breakneck pace! If you really want to kill Coren this year -- and I'd advise doing it, because he drops ilevel 470 stuff this year -- you've got until mid-October to reach level 89.
The Brewfest meta Brewmaster is required for the year-long What A Long, Strange Trip It's Been, so you'll want to get this done if you're working toward a Violet Proto-Drake.