Have one of those seven million jailbroken iDevices? Like it that way? Then stop -- don't touch anything. iOS 6.1.3 is poised to ruin your day, and there might not be any way to go back.
iOS 6.1.3 is only in beta right now, but when it does come out it looks like it's going to eat your jailbreak for breakfast and keep you from jailbreaking it again. Apple has fixed one of the five crucial exploits evasi0n needs to survive. One of evasi0n's creators, David Wang, explained the bad news to Forbes:
If one of the vulnerabilities doesn't work, evasi0n doesn't work. We could replace that part with a different vulnerability, but [Apple] will probably fix most if not all of the bugs we've used when 6.1.3 comes out.
So it's not the end of the jailbreaking line, but with each batch of patched exploits, the job is going to get that much harder. If you have a jailbroken device, don't install any updates from Apple without a little research. You should probably wait for word from the evad3rs themselves. [Forbes]