I've been kicking around and gradually prototyping an idea somewhat similar to greplin, but locally hosted. I originally thought of it more as a cloud archival system, as a guard against some dinky web service I use shutting down and locking me out of my data, but once you're collecting all the data adding really good search on top of it is a natural next step. Right now I'm aiming at distributing it as a VM image (because the dependencies and such are rather complicated), but some day I'd like to see it running directly on backup/NAS devices like the Drobo so that you could have a (roughly) "just plug it in" backup solution for both local files and cloud data.