Recently I noticed that the only sub $10,000 SAN that is on VMware's VAAI HCL list is the Synology RS3412RPxs SAN. This SAN doesn't currently support all the VAAI API's, but it does support ATOMIC test and set.
Their DSM 4.0 is really refined and the setup was very easy. I bought the RPxs model, because it has dual power supplies. I thought about purchasing a 10G NIC card and then load this unit with SSD drives (which is supported), but then I thought that it might be better and cheaper to load the unit with Seagate Enterprise drives at 500GB a piece. This will give me 10 spindles with smaller drives sizes, and hopefully giving me more iOPS at a lower cost. This unit fully loaded with drives using my configuration was only about $6,000!!
To get "Hardware Supported"for VAAI on ESXi 5.0, remember to setup a iSCSi file level LUN. This will allow ESXi to use the Synology for VAAI.
I haven't done much in regards of in-depth testing, but I'm currently running our highly utilized production Exchange mailbox store on it and it's running circles around our EMC VNXe that also has Exchange server running on it.
So far I recommend Synology, it's giving us features that the big boys only give us at $25k and above. Give me your feedback and questions.