As someone that just installed a dual 17" LCD flat panel system in an office, and then showed them the SSA, I can say that the first thing they asked for was a version of SSA that used both monitors!
Even on one monitor, the screen saver garners lots of comments when I demonstrate it, and I think a multi-monitor version would make it even better.
For reference sake, all the dual-monitor systems I've installed have been with Matrox Millenium cards, most recently the G450. Now that the Parhelia card is out, there is a possibility of having three monitors for your coding pleasure!
I don't know the mechanics behind programming for mult-monitor situations, but I do know that Matrox cards can treat the desktop as being double wide in resolution (2048x768 for example), but still keep the Windows taskbar and other functions appearing primarily in the first monitor. There are other modes, but I would wager that most people run it in that double-wide setting.
On the surface, that would appear to force SSA to support resolutions that have a 2:1 (or now, 3:1) aspect ratios to handle the dual-monitor situation. As luck would have it, I'm sure that every dual-monitor video card manufacturer does it just a little differently, which are all different from the default Microsoft way...