I tried restoring my iPad 3 on 5.1.1 with no luck.
I kept getting "APTicket flashed cannot be re-used." My understanding is, if you're on 5.1.1 and want to restore back to 5.1.1 you can using Redsn0w, if you DIDN'T update to 5.1.1 via OTA and have your shsh blobs saved (locally or on cydia.)