Summary: Installation was, literally, a no brainer and with OSX and it wasn't even necessary to load the drivers from the accompanying CD. The only "requirement" was to change a 2-way switch setting atop the card (PC/MAC) and even so, it would only preclude seeing the Apple logo at boot up. I am using in a 2009 Mac Pro tower and the graphics output is great. I bought it primarily to allow me to run Final Cut Pro X.
Summary: My 2008 Mac Pro eats these things every 2 to 3 years. I know there are other graphics cards available (for twice the cost) but the GT120 has been ok. The problem seems to be dust, I keep a can of air handy and when the inevitable shutdown occurs - a squirt cleans the card to allow a few more months of service. I understand the GT120 has been discontinued - so I'm thinking about another type when this new GT dies.
Summary: Got this for my Mac Pro. It had a mini display port which I got tired of the Apple mini display to DVI adapter going bad so I decided to just get another graphics card. Had never opened the case before but only took 5 minutes to install. Rebooted and it just worked.
Summary: I bought this card about a year ago for my 2008 Mac Pro and it's been working fine, even though the official line is that a 2009 Mac Pro is required. No problems even after adding a second monitor, one on mini Display Port and one on DVI.