I'm not really sure what Blizzard could have done differently. These boards (let alone the official forums) were absolutely up in arms about how poorly public testing of raids was done in TBC beta. You could argue that they overcompensated in 2.1, but I don't really agree. By all accounts, there are
still bugs in several of the later encounters (adds evade bugging on Vashj, corpse despawning on Curse's Hyjal kill, only one BT attunement item dropping), even with the extensive testing.
I guess one interesting option would be to contract with a guild or two, have everyone sign an NDA and maybe get some token amount of (real world) cash in return for access to "Uber New Raid Instance #8". Blizzard would get decent test coverage, and presumably the threat of lawsuits would keep leaks to a minimum. I can already imagine the cries of outrage on the WoW forums, though. "Bliz favors Death and Taxes! Their PTR experience is the only reason they killed Boss X! We almost have Zul'Farrak on farm and woulda been first if not for this SLAP IN THE FACE!"
