So you've used Blackra1n? I did too, and it works great. Simple and easy.
However, if you use Blackra1n and Winterboard, chances are you'll enter a state where you iPhone gets stuck at the Apple logo with no chance at fixing it. Has happened with numerous people so far, including myself. Here's how to avoid this -
However, the above fix will not work unless you first enable your iPhone to work with the iPhoneBrowser. Blackra1n doesn't enable the proper service to be able to use iPhoneBrowser, so you have to do it manually. This is described on the iPhoneBrowser's homepage: iphonebrowser - Project Hosting on Google Code
So, to summarize - if you use Blackra1n, you should make sure you iPhoneBrowser is working before you install anything. Once it is working, if you get to the point where your phone is stuck at the Apple logo, you can use iPhoneBrowser to recover.
So it's a blackra1n bug?
Should we expect an update to this JB
I gotten my WB to work by just installing Cydia after JB, and not others, and by manually powering off and on my phone and not using the Cydia Reboot device option it gives after the install...