I had some teething pains getting the ESXi server running (I think some hardware incompatibilities) but for now (knock on wood) everything is stable. At one point i was really considering switching over to an Intel server to avoid comparability issues, but that comes at the price of new hardware 🙁
http://lime-technology.com/forum/index.php?topic=22553.0 :Discussion of running UnRAID under ESXi on an AMD platform.
For future expansion, an eight port HBA SATA card would be welcome (to allow for more drives)
http://lime-technology.com/forum/index.php?topic=43026.msg410578#msg410578 :A great post on SATA HBA controllers and their performance