As you are aware the iOS 5.1 has been released and many of us are updating it without knowing that ios 5.1 untethered jailbreak is not available. Also you may need to degrade your firmware if you wanted to check features of new ios 5.1. I recommend you to save your SHSH blobs before updating your devices to ios 5.1. iFaith is a good tool that you can use to save SHSH blobs. The new version 1.4.2 of iFaith supports the recently released iOS 5.1 plus also includes some bug fixes from previous version. Below is the download link for iH8sn0w’s iFaith which is used for downgrading to previous versions of iOS firmware. You can read here how to save SHSH blobs.
iFaith v1.4.2 for Windows