CONS:
*I also have the same battery percentage drop problem. I had the same problem in Gingerbread though. And this problem happens at random at any time too. Suddenly the phone will not respond and I can not lock the screen, buttons won't respond, etc and will either restart on it's own or I have to hold down the power button until it hard restarts. My wifes phone(same model/update) has this issue as well with different apps and stock launcher. I downloaded ICS by entering my phone model/SN before the release date and updated my wifes phone a few days later the normal way.
*Battery life is about the same, sometimes worse - I am trying to track it down with Better Battery States, CPU Spy, etc to see if I can find out why it drains so fast(usually 35 to 40% at 6PM, off charger at 7:30 AM). I found that the Fox News app was constantly staying on in ICS but acted normal in GB so I deleted it.
*Slow to open apps/screens. Not all the time but sometimes it will become unresponsive and take a few seconds before it does anything. Locking the screen and waiting a few seconds will help.
PROS:
*USB Support for small devices!! I could plug in a thumb drive and mouse before but now I can plug in an external SD card reader(and SD card from DSLR) to view, edit, send files while out on a photo shoot! This feature alone is worth dealing with the hassles above! (And fun to show off in front of friends with iPhones too...)
*Task manager swipe feature is convenient!
Overall, I like it!