After having Big Problems getting mail on my jailbroken 4S running 6.1.2, and thinking, due to ever-present download scams for jailbreakers, that one existed for 6.1.3, I upgraded. I don’t have my ROMs signed for 6.1.2, because I didn’t get them while Apple was still signing them, so I’m fucked until they come out with a new JB, and that may not be until iOS 7.0. In the process, I’ve probably lost about 1/4 of the Apps I actually use, although some of them still work on my iPad. The worst, though, is losing tethering. I’m now 100% dependend on wi-fi access.
So if you’re jailbroken using 6.1.2 and thinking of upgrading, as of this date, there is *no* JB for 6.1.3. Don’t do what I did and get fucked.