Well... my 2 cents:

Team: Paly tank, Holy Priest, DPS hunter mage and boomkin all hit 80 about 2 weeks ago.

I geared up just doing the first 2 bosses of TOC for about a week (skipped black knight as I just cant seem to get straffing right yet). Sure... i could have wiped a ton and kept at it, but figured I should gear up first.

After a week of that (about 20 runs), i decided to give Heroic Gundrak a shot. Breezed though the entire zone. Then UK and Nexus were all a breeze. Think I will farm them for a while before moving on. I find those heroics to be a TON easier than I thought they would be.