You'd probably be more informed by simply goggling your question as I did, It seems their is a lot of information on it.
Most of it is about using it for medical imaging uses, reason being that it's just simply overkill for the computations needed for gaming
One site clustered 4 dual GPU's in order to render MRI images from a single computer, speed of the rendering was the reason for clustering the 4 dual GPU's.
Then theirs the cost and the fact that special code had to be written to take advantage of the calculations needed for what they were trying to achieve.
Also for gaming purposes their are already boards out that can handle 4 GPU's( which would be considered a cluster of sorts) but you also have to take into consideration bottlenecking since all calculations have to be processed through your CPU and RAM not to mention the game can only be rendered to whatever limit it has been written for.
For instance once you have the game set at all the highest settings more GPU rendering power is no longer needed.
As you question stated you've seen this being used in other fields, but if you think about it it's already being used in gaming when you can run TRI SLI or Quad SlI, which is a cluster of GPU's in itself.
So my GUESS is yes you can use a cluster of GPU's since Quad SLI is available on certain MB's
But then again I could just be way off base that is why I suggest you search for your answer yourself (not trying to be rude) http://www.google.com/search?sourcei...27s+for+gaming
I just think you could narrow down what exactly your looking for in an answer.
Caution I only read a couple of articles on this so please take it easy on me I take corrective criticism well as log as it's done well. Thanks. Fabe