Hot on the heels of Gruul's hotfix, Magtheridon has been adjusted (read: nerfed) as well:
The Magtheridon encounter has been rebalanced to be somewhat easier and should now better keep to proper raid progression.
Reprorts have it that although Mags himself hits harder now, the adds have less HP (120k less, according to one poster). Magtheridon was significantly harder than Gruul, who he was in theory meant to be on par with; hopefully this, as well as the Grull fixes, help make beginning BC raiding a little easier. I mean, I'm all for having to work for your epics, but I think most of you will agree that the beginning of the new endgame was a little too much like a brick wall.
I'm pretty far from fighting Mags myself. Apparently he has five adds, who as in most add-based fights represent a significant part of the difficulty of the encounter, so nerfing them should go a long ways. However, based on the run-down over at BossKillers, it still looks like a pretty involved fight. Come to think of it, doesn't Kel'idan the Breaker, who is positioned directly above Magtheridon in the Blood Furnace, have five adds himself? That fight's a cakewalk, of course, but the parallelism is interesting.