I am having the same issue. What some people are failing to understand about obnoxiousacorns' original post is that she is trying to boot tethered through redsnow and it is still getting stuck at the boot logo. I successfully jailbroke as well several times on 4.2.9, and when you reboot with redsnow tethered it reboots fine. The problem arises once you install an app from Cydia that requires a reboot such as MyWi or My3G for instance. Once one of these is downloaded they require a reboot to work. Once I reboot tethered through redsnow after installing one of these apps the phone gets stuck on boot logo and there is nothing left to do but restore. Unfortunately I had to upgrade to 4.2.9 because my phone froze while on 4.2.8 jailbroken and I had to restore. iTunes would not let me restore using my custom 4.2.8 file because 4.2.9 was out and I did not have my SHSH saved. Does anyone have 4.2.9 jailbroken and able to use Cydia apps after rebooting with no problem?
Dont waste your breathe there is no untethered JB. Whatever your friend did he didn't update a firmware through cydia. I'm trying to save you from the ridicule. To the poster who stated the reboots that's what a tethered JB is. You must plug your phone into the computer everytime you reboot or your going to come up with the same problem everytime you install a cydia tweak/app. So I suggest you don't do it.