In my case, the update was pushed to me (I'm in London).  It actually does not say 4.2.1 but just 4.2 which actually confused me for a while coz I was on 4.2 already.  No problems encountered so far.  I think the best way to address issues being experienced by some is to back up everything with Google then do a factory reset.  Didn't have to do this, though.