Two recent high-profile game releases have generated a bit of buzz within the multi-monitor community.
There is absolutely no reason any developer to lock out features based on which video card you purchased.
First was the release of The Witcher 2: Assassins of Kings. This title was "sponsored" by NVIDIA with their "The Way It's Meant To Be Played" (TWIMTBP) initiative. By all accounts the game is a great title, and offered superb "Surround" support. However, it doesn't support TripleHead via the Matrox TripleHead2Go or AMD's Eyefinity.
There is absolutely no reason any developer to lock out features based on which video card you purchased. This type of behavior segments and already small market and will slow the adoption of multi-monitor among users. Why would a user invest in any multi-monitor technology, if they have to worry about developers not only supporting multi-monitor, but their choice of multi-monitor technology.