WARNING: IF you already FXZ'd OR took the JB update, you can SKIP THIS POST AS IT DOES NOT APPLY TO YOU.
Alright, so, here's some new info brought to you by timmy10shoes....
IF you are on stock 246 ICS, don't care about root (for now), and want to "try" jb before you buy, there is now a way to upgrade WITHOUT locking you into JB. With this method, you will be able to downgrade back to ICS (although keeping your data is probably not going to happen...at least you can get back to ICS if you choose).
WARNING: Failure to follow these steps EXACTLY will cause you all KINDS of problems that *I WILL NOT HELP YOU WITH*. Use at your OWN RISK.
o) Grab the cdt.bin from the 246 FXZ and set it aside. Make SURE you grab the right file. This is absolutely critical and your failure to do so will be the make or break point as to whether you can downgrade or not. DO NOT SCREW THIS PART UP.
o) Remove the 246_FXZ from the House of Bionic (HINT rename it to 246_xxx)
o) Install the 98.72.22_FXZ to the House of Bionic
o) Replace the cdt.bin in the 98.72.22_FXZ with the file you set aside from the 246_FXZ. Again, DO NOT SCREW THIS PART UP or you will NOT be able to downgrade!
o) Use the FXZ Keep Data option
Enjoy JB.
To downgrade, remove the 22 FXZ from the HoB and replace it with the 246 FXZ and do a FULL. Trying to Keep Data will likely result in a boot loop.
I take NO responsibility if this screws up your phone.