The feedback we have received so far has not been too positive on using any caching devices. Generally the consensus has been that these are on the bleeding edge and vendor support and certification has not been established yet.
The recommendations we keep getting are along the lines of using a SAN that has some form of SSD caching, SSD trays, dynamic tiering, etc.
I personally think keeping your cached I/O on the host is better than hitting a cache across the network so I think this market is primed to take off, but it doesn't seem to be picking up too much steam yet.
Kevin