If you also google the issue it comes up in a lot of previous posts, but they've since been deleted off the battlenet forums.
Having the same issue as these people. Using a Nvidia GTS 250. Freezes, screen goes black, monitor sometimes goes into sleep mode, get back in game dead.
I've done a clean install of only the graphic drivers for the beta and last 4 versions of drivers.
GeForce 301.24 Driver BETA
GeForce 296.10 Driver WHQL
GeForce 295.73 Driver WHQL
GeForce 285.62 Driver WHQL
Latest games I've played WoW & Skyrim never had this problem.
Issue usually starts up 30 minutes into playing, then persists every 2-5 minutes, making the game unplayable.