You know, Derek, that's a good point... I've perused Climbcation before, and I think it's a cool site, but it's limited to the areas that the webmaster put in there by hand.
OTOH, each area on MP already includes average weather data, as well as a chart showing popularity of an area by month. (I'm assuming that's from users' ticks?) To be able to incorporate that data into a search function to allow one to discover new areas by season would be pretty sweet.
I'm thinking something along the lines of the route search function, but for entire areas. It's probably more of a vertical search function though, so I'm not sure how easy it would be to implement. You ultimately want to be able to search for areas with specific types of climbing (sport/trad, certain grades, etc.), that are also popular during a given month, or have certain thresholds for high/low temps, rainfall, etc.