Tho they have nothing to do with "the blues", musically or otherwise, and they are not actually blue, Blue Moons are pretty rare.
A Blue Moon is the second full moon that occurs in a month. Given the 28-day lunar cycle and the roughly 30-day average month, indeed it is an unusual occurance. It pretty much requires one of the 31-day months (like this month), and the perfect timing of a full moon on the first day or two of the month (like this month...)
And why yes indeed, as you've probably guessed, we will have a Blue Moon this month!
The next one will not happen until 2015. So all those things you were putting off until a Blue Moon? Well this is your month...