Prepare for a blitz game?

Perhaps this is a stupid question, but I was thinking a lot about this in the last time: do you prepare against an opponent when you play a blitz game? I mean, not in a tournament. Until now I just take challenged everybody and play, without any preparation. 

I began to think that some people prepare because when I begin to play a new opening (like 1.b3), several opponents seem not to know how to play against this and usually are losing material already in the first 4 to 7 moves or get a strategically bad position. However, after a couple of games it seems that people (with a similar range) begin to play better through the opening.  

It is mainstream chess knowledge that reviewing games you play in order to improve is a key element if one wishes to improve. I imagine that applies to games at all time controls including Blitz.