If you’re the type of user who needs to have your fix of apps, tweaks and other goodies only available to jailbreakers, through Cydia (being the most popular option) or otherwise, then you’re likely going to want to hold off on upgrading to iOS 5.1 when it’s released. As you may or may not know, an untethered jailbreak for iOS 5.0.1 has recently been released (for A4 iDevices as of now, while the A5 jailbreak is still being worked on) thanks to pod2g‘s “Corona” exploit.
Unfortunately, it has been discovered that this exploit has been patched as of the third (and current) beta of iOS 5.1, meaning that unless another exploit is used once iOS 5.1 comes around, there will likely be no untethered jailbreak for that version of iOS 5. That may be some seriously bad news for jailbreakers, especially those with A5 iDevices that are incapable of even performing a tethered jailbreak (A4 iDevice owners are lucky enough to have that option on iOS 5.1 thanks to a bootrom exploit even if another untethered jailbreak is not released).
So, what does this mean for you as a user (and, I’m going to assume, a jailbreaker)? It means you should probably stick to iOS 5.0.1 when 5.1 is released, and you should upgrade to 5.0.1 now if you haven’t done so before Apple releases the update publicly and stops signing 5.0.1. It’s best to assume right now there will be no untethered jailbreak on iOS 5.1 and be pleasantly surprised should one be developed, rather than take the risk and upgrade in hopes one will be released. A5 iDevice owners are again especially encouraged to avoid updating as there is currently no way to downgrade their iOS version.
Even though iOS 5.1 is promising some exciting new features—such as a supposedly permanent fix to the dreaded battery life issues users are still suffering from even on iOS 5.0.1—you will have to assess whether those are worth risking the loss of an untethered jailbreak. As for myself, being an owner of the original first-generation iPad which I’m going to assume will become discontinued after the launch of the third-generation iPad, it is likely that iOS 5 will be the last major software update I will be able to use, and I know I will definitely not be losing out on having an untethered jailbreak.