New day, new TinyUmbrella update. This tool allows you to save your SHSH blobs, so you can downgrade your iOS devices to a previous firmware even after Apple stopped signing that particular firmware.
TinyUmbrella v4.1.13 was updated to work with 4.2b3 for all relevant devices. Go ahead and save your iOS 4.2b3 blobs , because they might help you with future untethered jailbreak.
Download TinyUmbrella for Mac, Windows and Linux here