I'll push it a little on the flats/downs or with a favorable wind. But for the most part I'm just cruising. This interesting thread prompted me to look up my speeds which I have in Garmin Connect since I started tracking about a year ago:

2014 Avg Speed
Feb 16.6
Mar 17.0
Apr 17.4
May 17.4
Jun 16.0
Jul 16.8
Aug 16.3
Sep 16.3
Oct 16.8
Nov 16.5
Dec 16.2

2015
Jan 15.9

I'm not sure why the big drop from in June. And I've definitely been slower over the colder months (more gear I guess). It will be interesting to see if I trend back up or not without necessarily trying to.