One of my computers is a Mac Pro, which I've been very happy with, except for the restriction of using "Mac" versions of Pci-e Graphics cards, which are typically more expensive than their PC counterparts.
I had been running the machine with an Nvidia GT8800, which was a fairly powerful card, but was dismayed to see all the new cards coming out for the PC which were faster and cheaper.
There are ways to "hack" OSX to get it to accept a non-Mac graphics card but I was loathe to mess around with a working machine.
So I was very curious to read that in Mac OSX Lion (from 10.7.2 I believe), you can install a standard PC graphics card and a driver from Nvidia, and it just works :-)
I thought I would give it a try. I first installed the Nvidia driver for OSX 10.7.3 from here. I then installed an Nvidia GTX550ti graphics card. I chose the GTX550ti as it has a lower power requirement than some of the faster cards and I didn't want to overstress the power supply in my Mac Pro.
I crossed my fingers and powered up...
There were a few moments of doubt as there is no boot screen or spinning icon as the machine starts, but then the desktop appeared and everything was working!!
I also run Windows via boot camp and rebooting into windows I got the "found new hardware" message and the drivers for the graphics card were updated.
I haven't had a chance to run any serious benchmarks yet but I'll have a play with the system this weekend and see how it's running. First impressions are very good, the system seems happy and the graphics performance is definitely better. The GTX550ti only cost me €150 :-)
NB: Apple updated Lion to OSX 10.7.4 which broke the Nvidia driver, but Nvidia released a new driver here which apparently works. I haven't tested it personally. I'll wait until any other issues with 10.7.4 have been identified.
UPDATE: Last night I took the plunge and updated my Mac Pro to Mountain Lion 10.8The GTX550ti is supported as standard, without installing any drivers from Nvidia, in fact the drivers installed by OSX show as driver version 295 which is newer than the 270 drivers for Lion.
UPDATE 2nd August. I have had some instances of graphics corruption in Mountain Lion which I didn't have in Lion. I will keep an eye on the Nvidia site to see if they release updated drivers for Mountain Lion. The built in driver has a release number of 295 so it is behind the 300 series drivers that are current for other platforms.
UPDATE: It seems the GTX550ti has problems in Mountain Lion relating to sleep and recovery. For the moment I recommend you do NOT use the GTX550ti in Mountain Lion.
UPDATE 29th August. I have ordered a GTX660ti and will put up a new post with my experiences with that.
I have also found a cheap source of Mac Pro GPU power cables, you can order them from ebay here. I ordered two and they arrived the next day!
This post is getting quite old now, please see my other posts for more recent information.