The FW800 port is more than adequate to connect a mechanical hard disk. If you just want to migrate data I would go that route. There is always something useful you can to do with a good USB/FW800 enclosure.
One advantage to waiting for the TB enclosures though, would be the daisy chaining capabilities...so in theory you could still connect your mechanical hard drives for storage and backup use as well as the new smoking fast SATA III SSD drives hitting the market now.
I wouldn't wait for TB to get a good backup solution in place though.