I updated without any problems other than getting the ATV2 into DFU mode! In use iReb4 to help me determine if I have successfully managed to get into DFU mode. On my system I find that I need the Power plugged in while getting into DFU mode, but that once I am there it needs to be removed to avoid an iTunes restore error. Other than that everything went through without issue. One thing I did notice is that this time around there is no SeasonPass item added after the jailbreak so it is less obvious that it has worked. However I then ran teh ATV2 software on my PC and it was able to find and install the ATV Black software.
Another thing - Overflow does not work with the latest Apple firmware so your menu bar gets a bit cluttered. I noticed that the ATV Mainainance option no longer gives the ability to hide Menu items - I assume that this is probably related to the Overflow issue.