http://www.sourninja.com/dualwield/ I've pre-ordered one of these for my Xserve as freeing up a PCIe slot will make my life a lot simpler, but they would be a cheap and flexible option for iMac owners with flaky graphics or just after a graphics boost, or it could even be an insurance policy for an older machine against the graphics falling over. These are on Kickstarter with only a few hours left to go and if I were an iMac owner with a penchant for tinkering I'd be mighty tempted to get one. I hope these don't end up being vapourware...