All these numbers are according to sportsdatabase. Can't confirm the accuracy of these numbers (and obviously a few of these results depend on line shopping and such), but in general it looks like favorites have done quite well the past few seasons.
2008 Playoffs:
Favorites
47-37-1 ats
2009 Playoffs:
Favorites
42-40-3 ats
2010 Playoffs:
Favorites
49-28 ats
2011 Playoffs:
Favorites
37-43-1 ats
2012 Playoffs:
Favorites
50-32-1 ats
2013 Playoffs:
Favorites??????????
The total record from 2008-2012 is
225-180-6 ats (55.55%)
And the only 2 games I bet this weekend were two dogs