This is the feature request thread. Let me start off with some doozies:

Snapshot merging so you can make an active snapshot into a regular, linear logical volume (FC, iscsi, or NAS). This is how it ought to work already. Would make snapshots twice as useful. There's a relatively usable BETA patch of this for LVM2 already. Read more here: http://kerneltrap.org/Linux/LVM_Snapshot_Merging

NAS data deduplication: here's a free, open-source project that works on linux here: http://www.lessfs.com/wordpress/ But probably nothing will come of this project. Will probably have to wait until btrfs or tux3fs add deduplication. Also, ZFS will add support for deduplication, so maybe you could use ZFS in userland via FUSE? Sounds too cludgy to me.

block-volume deduplication (i.e. iscsi or fibre channel volumes): can be implemented on top of "lessfs" or btrfs in the future, see above.

NAS autofailover: I know this is already in the pipeline.

PLEASE add your own suggestions! And comment on features you'd like to see.