The company I work for, R Systems (http://www.rsystemsinc.com/ http://www.rsystemsinc.com/), basically does this. We own and admin several medium-sized compute

The company I work for, R Systems (http://www.rsystemsinc.com/ http://www.rsystemsinc.com/), basically does this. We own and admin several medium-sized compute clusters (200-500 node clusters) which are rented out to customers who need a lot of compute on a temporary basis. A lot of what we do is heavily custom, and we provide a lot of support for our customers, but we still typically beat Amazon on both price and performance. EC2 might work nicely for embarrassingly parallel workloads, but they don't have Infiniband available if you're latency-bound... :)