Apple just released a nice support doc detailing AirPort Extreme (802.11n) USB drive support. Looks like you can use HFS+, FAT16, or FAT32 with a 512-byte block size. (Apple notes that not all USB storage devices use 512-byte blocks.) No RAID volumes and no partitions allowed. (Update: At least that’s the official word. In the comments below, Jason reports that he’s had no problems using a 2-partition disk with his new AirPort Extreme.)