Anyone have any knowledge or experience to comment on whether a Windows machine would benefit from a dual SLI graphics card setup?

I use 2 monitors; one a 30 inch Eizo and a second 22 inch. I'm designing a new Windows 7 64bit machine and am unable to find any info on any possible SLI advantages for running CS4. I don't run any 3D software or do gaming, so my intuition would be that there is no advantage to SLI. The majority of my Photoshop files are derived from a 39MP Hassy H3DII-39 -- so they are quite large -- and I'll be moving up to the 50 MP model within the week, so they won't be getting any smaller .

My computer came with a pair of nVidia 3800GT cards (512MB each) and an Intel quad core CPU. I use a 30" NEC monitor, and use CS4, Lightroom and DXO depending on what I am doing. I also use Photomatix as I shoot lots of HDR. I have worked with and without SLI enabled and have not found any real world difference (I have not made actual time trials, though). I suspect I would do better with one 1Gb graphics card.

SLI is strictly for 3D (i.e. gaming or 3D software) SLI helps a lot when using 3D CAD software, I use softplan and there is a noticeable difference when rendering the 3D images, but while running Photoshop, the Nvidia 4800 or 3800 are great cards and they are even great cards for the 3D software.

Thanks for the input gentlemen.
I did find additional information from the NVidia SLI forum; bottom line -- no effect or advantage for CS4 Photoshop rendering.
CAD software and a few games which are specifically coded for using SLI do indeed benefit.
I've decided on one NVidia GTX 295 for my new system; with 1792 MB of GDDR3 memory it's probably overkill, but it will presumanbly keep me happy for a couple of years.