We also back up to LTO tape. We have LTO-4 drives at work. Projects are moved to a mirrored NAS for near term storage then archived to LTO tape from there, on a schedule. For P2 and XDCAM-EX footage we offload cards directly to both the NAS and local RAID. We used to use BD-R to archive but we prefer this NAS to tape arrangement - much faster/cheaper and we have lots of redundancy both locally at the workstation and within the NAS. The tapes are bullet proof, *excellent* error correction, large capacity and fast (though we usually run backups overnight).
As far as price, yes new LTO-4 *is* expensive, however I just picked up two LTO-2 drives off ebay for about $80 each. I'll use one in my home studio hanging off an old G4, running Ubuntu as a simple RAID 1 NAS / backup station. Now I'll have the same industrial quality backup for my home network. The other one is kept as a spare (a no-brainer given the price).
LTO-2 is good for 200-400GB per $30 tape and the LTO spec (which is open source unlike DAT or DLT) specifies that you can read back from at least two generations of future drives. The tape data *mounts* so copying from LTO-2 to any newer LTO flavor in the future will be easy (our to some other BU option - the *cloud* maybe??).
Roger Hendrick
The Airship Factory
http://www.airshipfactory.com
HD Video Production - Blu-ray Authoring