I just recently went from GB to both ICS and JB.
I personally was encountering some errors with the JB like the Play Store not working and some minor issues.
I have for the time being settled on an ICS that is really rocking for me.
I would recommend the following:
First get something like "Go Backup Pro" or "Mybackup Pro" and do a full backup of your phone to your external SD
I would also recommend getting the infuse toolkit from here
MTD issues - xda-developers
You will need to copy the toolkit to your internal SD
Use this in CWM to install the toolkit and do a full ROM backup as well as a one time backup of your EFS to catch your IMEI information
Next you will need to make sure you have GB Bootloaders or you will get the rainbow screen when trying to go into recovery mode.
The above was particularly tedious until someone told me about the Heimdall One Click:
[AT&T] [ROM] [UCLB3] Heimdall One-Click Return to Stock + Easy CWM Installation - xda-developers
You will flash this twice per instruction and the second time around you will click to install the GB Bootloaders.
You can then download CWM from the market or Odin flash the following ROM to get back your recovery
[ODIN][UCLB3] AT&T 2.3.6 Gingerbread with root and CWM recovery option - Infuse 4g - xda-developers
My personal preference here is Option C
Below is where you will get what I would recommend as a solid starting point for ICS
[Firmware][ICS]UNOFFICIAL CM9 for the Infuse 4G (07/28/2012) - xda-developers
Download the 07/28 ver of cm9
Download the appropriate gapps
(make sure the gapp file has ics in the name)
Follow the steps verbatim (VERY IMPORTANT)
From here its very straight forward if you want to go to JB.
Remember BACKUP BACKUP BACKUP
I always have a point to return to. You decide what and where you want that to be and you can have multiple spots.
As long as you have the Odin ROM I mentioned and or the Heimdall you can return to a stock ROM.
Hope this helps...