A lot of hype has gone in to pushing SLI and CrossFire. Multi-GPU platforms have been touted as the “next big thing” in gaming performance, and both camps offer many ways to get it done. How many people are actually biting into it, though? According to a survey done by Valve (which you've likely participated in if you use Steam) is revealing that only a minor 1.5% of gamers are using multi-GPU systems:

Only about 12.7 thousand of 850 thousand of respondents – or about 1.5% – had a multi-GPU personal computer (PC) with either two, three or four graphics processors, the stats at Steampowered web-site reveal. Given that approximately 49.42% of Nvidia GeForce graphics adapters in possession of Steam users are either AGP or PCI, whereas PCI Express was adopted by 44.68% of gamers, the share of multi-GPU systems among Nvidia GeForce-based PCI Express computers is more significant: 6.88%.
Even more interesting, of that tiny fraction, around 96% of it is GeForce-based, meaning that Crossfire is really hurting. The survey started with data collected as early as November 2006, which is not so long ago that SLI wasn't already embedded into every advertisement that nVidia and their partners make. Why aren't people biting? Aside from the obvious reasons of much higher costs and low support among game developers, that is.