Well, you did ask this question and the paper from Dell gives that answer...
How many instances can I realistically expect to run on each card (GRID K1 and K2) assuming 1920x1080 single monitor resolution?
I have been involved with quite a few customers with these technologies now and if its something I have learned is that you have to put a real user in front of the desktop and let them have a say. Something that looks good for you and me might be totally useless for a professional designer for example.
I've seen the marketing material regarding AutoCAD, but what about Adobe and ArcGIS?
Adobe is a company with many products, anyone in particular?
ArcGIS I have not tried.
Are the GRID Certified Servers really the only platforms GRID cards will work in, or will they work in other server models, but just aren't 'certified'?
The real issue is the the GRID cards do not have an active fan on them so the chassis have to be able to cool the GPU properly.
You do not need a GRID-card but you could instead use a Quadro card. Some models are supported with some technologies.
For example the Quadro 4000 (Thats the one I have) works both with vSGA (shared) and vDGA (dedicated), that one have an active fan and works in most servers/desktops.
// Linjo