We have had the XIV since August 2009, and are very pleased with it. We are mainly a HDS and IBM shop (well, on the storage side anyways). We were looking at the AMS2500 or the XIV, and of course all things come down to cost and the XIV was much less than the AMS2500. Currently, we have VMWare (300 VMs), MS SQL and Oracle using the XIV. Prior to the XIV we had our Oracle and MS SQL applications on a AMS500 and a AMS1000 and noticed performance gains between two to three times faster.
Now we also have a HP EVA 6000 and that is solely used for one application only. It also works fine and is somewhat similar since it also uses storage pools so all the disk are busy rather than dedicated LUNs to certain host(s). I guess the big difference between the two is the XIV has no RAID Array (1MB extents are copied to other disk in another module for redundancy) and uses SATA disk and our EVA uses RAID 5 with FC disk. The funny thing is the EVA 6000 with FC disk is actually lower performer than the XIV and the rebuild of a failed 1TB disk takes us about 15 minutes to do. To be fair though, the EVA we have is two years old so a newer EVA would be a better perform than the one we have.
So, in my book, I would choose the XIV for cost, performance and is grid based. I think grid base storage arrays is the future and many other vendors also are going that direction.