The consistency debate often arises when one goalie has a lot of shutouts and another has very few. Luongo vs. Brodeur in 2006-07 is one example that comes to mind. If two goalies have similar overall season stats and one has substantially more shutouts, that simply means that he must also have had more bad games.
However, I have noticed that this season there have been a number of goalies who have had absolutely fantastic months. Roberto Luongo was almost unbeatable in November, but wasn't nearly as good since returning from his groin injury. Steve Mason was dominant in December, but was been merely average in 2009. How much should a great month contribute to the overall total?
On the other side of the coin, what about one terrible month? How much should a goalie be penalized for that? Henrik Lundqvist apparently has some issue with performance in the month of December. In his career he has an .891 save percentage in December, compared to .921 in all other months combined. This year Lundqvist remained true to form, stumbling through the Christmas season but otherwise playing pretty well. If we take out his December numbers, Lundqvist ranks up near the league leaders.
I decided to go through and knock out the best and the worst month for some of the goalies who might get talked about in terms of the Vezina, and see what was left. There were a few goalies who were downgraded by this method (e.g. Mason, Roberto Luongo, Cam Ward, Pekka Rinne), and some that got a boost (e.g. Lundqvist, Marty Turco).
These numbers are unadjusted and as such are very team-dependent, so as always take that into account. However, if you think consistency is something that should be rewarded, then you should probably go with Tim Thomas for the 2009 Vezina Trophy.