With the latest GB, my mage has noticeably improved his harvests per day.. I have my mage using:
1 - mage armor/mount macro
2 - smoker engy tool
3/4 - conjy food
6 - water ele
7 - sequence rotation macro with ice barrier, mana shield and mirror image (didnt put a reset on it)
8 - the usual sequence macro from bosslands 4.0.1 post..
9 - conjure food
0 - arcane int
- empty
= hearthstone
Workin out pretty well, since mage armor is always up through mount macro then mana shield is good to rotate with ice barrier, and mirror image when its up
I think it really varies based on their combat fixes per version of GB though, i've seen some GBs really make my mage suck for harvesting and others are just fine.