I had 9.04 Alpha 1 installed for a while because there was a bug in the stable 8.10 Nvidia driver with Compiz. I haven't updated it, though, and I think it is still installed on my old hard drive, so I will have to reinstall if I want to get the final 9.04.
Hopefully I can get my laptop to boot 9.04 off my external drive with eSATA so I don't have to mess up the partitioning on my internal drive (plus, I'm out of space).