I can't really say which release the really bad one is. 4.2 or 4.2.1. I don't remember having problems with my phone last week. I surely have them now. Interface doesn't react sometime or very late. SMS seem to arrive several time, I get the notice that there is a SMS but I can't read it right away. It appears after a bit. My battery is sucked empty far faster than before.
So something is wrong. Very wrong. I hope Google will fix this soon are there will be workarounds. Someone said Google Currents is part of the problem. I didn't use it before but just in case I activated it and then disabled the sync as recommended. But I don't think that was the problem. Saw that Xing Contact Sync was responsible for a lot of my battery loss. So disabled the sync for Xing today. Will know more tomorrow. As far as I know there wasn't an update to Xing.
Anyways: GOOGLE, FIX IT PLEASE!
I wish you well