I didn't notice any increase in impressions that I can't attribute to additional adgroups that I have added. I am doing some "New Year's" campaigns, and have added significantly to my number of adgroups.
What I did notice, yesterday, was a big increase in conversion ratio. Not to pre-Christmas levels, but a very significant increase.
I am pretty new to this, and haven't been through a holiday season before. So, I didn't know what to expect. I was hoping that the post-Christmas drop in conversion ratio was due to people being home with time to waste, and the fact that most (or much) online ordering is done from work.
Sure enough, yesterday - the first post-holiday work day - saw a huge increase in conversion ratio.
I think people are more aware today of company rules on web surfing. While they still buy things from work, they are less likely to do casual surfing or shopping around. But they will take 5 minutes between tasks to get an order in, just as they would think nothing of picking up the phone to arrange a doctor's appointment or call the plumber to arrange that remodel. (But wouldn't be as likely to call around looking for a good price on carpet cleaning.)
That's my theory, anyway.