Do Pros use compact cranksets?
While pro riders often change gearing or whole bikes depending on the nature of the race or the stage, you do sometimes see compact cranksets, particularly among domestiques in mountain stages or races.

A big-name example is Tyler Hamilton in the 2003 Tour De France. After crashing and breaking  his collarbone before the huge mountain stages he was unable to climb out of the saddle. FSA who makes compact cranksets and was a team sponsor set up his bike with a 52/36 crank; allowing him to climb seated.  FSA did a couple of releases and maybe ads about it - and I started to see a lot more compact doubles in local rides.

Just note - a lot of times you can accomplish the same goal (bigger and smaller gearing) by switching the typical 12-23 racing cassette for one that is 11-25 or 11-27 at a lower cost.

You can play around with Mike Sherman's Bicycle Gear Calculator to help you make a decision.