I'm going to get an E5660 to play with soon. I want to see what it will be like as a target for backup. Looks like a pretty good bulk storage unit, 10GbE interface with iSCSI, or if you want, you can do 16Gbit FC. I'm going to stick with the 10GbE, because I have a lot of ports on the Cisco Nexus 5596s and the HP Blade chassis is connected to that as well.
HP has their 3Par 4200 series, but it was a lot more expensive than the E-Series.
Waiting on the stuff to come in, then I'll post more.