I already stated several times that I really love ZFS file-system. Since I deployed it in production for backup and recovery of virtual machines, I had intuition how it works, but recent conversation on fuse mailing list turned out to have hidden gem in it: Keynote speech from Jeff Bonwick and Bill Moore at Kernel Conference Australia 2009. It's Solaris kernel conference (and has wrong title in program: Deduplication in ZFS), so I would never watch videos from it, but this one is well worth your time if you are interested in ZFS.
If you are wondering about ZFS performance, read VMWare + FreeBSD + ZFS soft-raid with SATA drives - performance. Yes, it's on FreeBSD which is great because, now I can compare performance (in terms of orders of magnitude) on different systems.
I have been using compression on my storage server for a while, and saw dramatic reduction in disk space usage, but didn't do any performance comparisons. On other hand, we have some idea about zfs-fuse performance on dial SSD so I will probably have to do some update to latest zfs-fuse from Ricardo Correia which recently moved zfs-fuse development to git.