I've had the machine a long time... last year upgraded 3 of the 4 hard drives and added more RAM. I'm planning to upgrade the graphics board next. Last night, I had the main hard drive fail, so I've now replaced that and have the machine up and running again, but have come to realize I can't upgrade to Mountain Lion or Mavericks. The machine runs GREAT for my purposes (photography and graphic design mostly)... but I'm at a crossroads of what to do. I was considering trading it in for another used, but later model. I can't afford the newest Mac Pro right now. I also read that it might be possible, with a graphics card upgrade, to be able to install Mavericks on this old machine. What experience do any of you guys have with that? Anyone have a link on more info I can read about it? Any help or advice would be appreciated. I love my Mac Pro. It has run like a champ for six years!