We have several M610s in our VM hosting environment, some clustered some as standalone hosts. The performance is great, particularly with the latest hex-core processors, and with 12 RAM slots you can get incredible memory density. We use these for our IO intensive workloads attached to a FC SAN for our top performance tier applications. It absolutely blows the predecessors, the M600 and M605 out of the water, and until the introduction of the M710HD was the most memory dense half-height blade.
The CPUs may be overkill for some apps, but when you need it they're fantastic.