One thing that does annoy me about RAID is the absolute need for matched drives. I really like the idea behind the Drobo, Windows Home Server, ZFS, and other solutions that can guarantee data redundancy on the volume without requiring identical sized drives. Hopefully these implementations will be mature enough by the time I do look to replace my ReadyNAS down the road. Similar concepts were starting to show up in enterprise storage too before I left that job, and it was really nice.