They have a whole programming tips section.
http://www.realtimesoft.com/multimon...d_graphics.asp
Downside:
OpenGL supports only a very small number of 3D cards across multi-monitors. Direct3D seems better supported. DirectX 8 of course preferred. :-P
Upside: Heck, I'd just been thinking of "dual head" monitor cards. (A single 3D video card that supports two monitors) The people at this site are into three and four monitors at once, doing long extended landscape views. To my eye though it looks ugly if the monitors aren't matched models.
The real reason to appeal to the high end: Free publicity. I'd say draw a line in the sand like "Only supporting two monitors on XP using dual head video cards" so high end freaks can run with it. Multi-monitor types are leading edge technology types anyways, this will just drop support headaches with scavengers who try to cobble together something just to see if they can. (And they'll always be able to run it single monitor mode.)