We recently had the opportunity to test a couple of the Fusion IO PCI-Express 640GB SSD cards http://www.fusionio.com/Products.aspx in a Dell R900 server, unfortunately time was against us and we were unable to do this. The Fusion IO SSD cards would dramatically increase the IOPS capacity and personally, I think they would be suited to storing tempdb.  I’m a bit cautious about using SSD for data and transaction log so tempdb seems like the best solution.