@TheSmokeMonster:
The DRM on MAS downloads allows you to simply copy apps between authorised computers, which is what I did to avoid a long and tedious download. The very same process worked just fine with Duke Nukem Forever, also on the MAS. I've raised a support query with Rockstar. If I have to, I'll re-download it, but there really should be no need.
It's not bad to play. Being a "Cider" port (basically they took the Windows game and wrapped it in code that lets you play it directly on the Mac) there's a performance hit that you wouldn't expect if it was a native game. This hit was even noticeable on my 2010 Mac Pro! For the price, I tend to suggest people just buy the PC game and wrap it themselves in the same way using free and legal software available at PortingTeam. At the moment their "wrapper" only works on Macs up to 10.6 though, whilst VC from the MAS definitely works fine on 10.7.
@ClayG:
I did, and have just checked again - no go. If they do update it hopefully they'll fix the ear-piercing high-pitched distortion that frequently affects the audio in the left channel. Complaints on this are rife in the reviews.