When you need to query by date you need to do something like this in the console:

db.trackings.find({'created_at' : {$gte: new Date(Date.UTC(2009,1,01)), $lte: new Date(Date.UTC(2010, 1, 16))}})

Its a huge pain to the conversion manually it would be nice if there was a API in the shell to do this to for us.