With the public launch of iOS 5.1 , the developers already warned the people not to update to the latest firmware, otherwise they will end up loosing their untethered jailbreak, whose exploits have been patched up by Apple in the new iOS. So , if anyone upgraded to the latest firmware by mistake , they had a chance to downgrade their devices to 5.0.1 as Apple was signing both the iOS together untill 4 days ago, when Apple stopped signing iOS 5.0.1 .
This affected mostly the A5 users ( iPhone 4S and iPad2 ) who can’t downgrade their device , even if they have their SHSH blobs saved . Though, there is an option for iPad2 users to downgrade to 4.xx via blobs but then he won’t be able to move to 5.0.1 as it is no more being signed by Apple, even if one has 5.0.1 blobs saved. While the users of iPhone 4 , 3GS and iPad 1 can downgrade their devices using SHSH blobs and custom firmware signed via iFaith and Redsnow but that is also not an easy task to perform.
For now, there is a tethered jailbreak available for the A4 and lower devices using RedSnow and SnowBreeze, but since it is a tethered jailbreak , once has to boot tethered again via RedSnow as a restart looses the jailbreak , which is a big headache.
But there is good news, as the Chronic Dev Team and the famous iOS 5.0.1 hacker Pod2g have started working on finding the vulnerabilities in the new iOS to develop an untethered jailbreak on 5.1 .
Also, he hinted that we may hear some good news from the other famous iOS hacker i0n1c regarding the jailbreak.
Source : Wiki JAilbreak