Last week Chad Versace of Intel sent the final patches into the Mesa development list for enabling HiZ support on "Gen6" (Sandy Bridge) after landing the final 41 patches. While HiZ will be turned on for Sandy Bridge soon as the patches hit the Mesa Git master repository, it's not being enabled yet for Ivy Bridge (Gen7) due to a "mysterious performance regression."
HiZ support for Sandy Bridge means a big performance win. Back in September I showed some initial SNB HiZ Linux benchmarks with the advantages it brings. When the latest work lands in Mesa, I'll run some more OpenGL benchmarks.
The latest Intel HiZ patches can be found on the Mesa mailing list.