I was going to post in the already present OS X miner thread, but realized i'm tagged as a newb...
Basically I wanted to confirm what robin1979 (http://forum.bitcoin.org/index.php?topic=12360.msg219345#msg219345
) had found, that Mac OS X Lion (10.7) does indeed speed up mining for OS X users.
My Mac Pro with ATI Radeon HD 5770 in 10.6.7: ~103 MHash/s
My Mac Pro with ATI Radeon HD 5770 in 10.7 DP4: ~153 MHash/s
Note that in 10.6.7 I was using poclbm (-w 256 .... -v caused a massive slow down on this card). In 10.7 DP4, I was having issues getting it to compile and build (weird make errors, and haven't spent any time researching). So under 10.7, I was using Diablo. I know...not a perfect comparison, but at least us OS X users have something to look forward to in a month or so!