A bit of technical stuff and a digression:
There are many different definitions of a blue moon but the most 'official' one is
not the sort of Full Moon that happened tonight, instead it is when there are
four full moons in a season (i.e. between March 21 and Jun 21, or Jun 21 and Sept 23, etc. etc). The Blue Moon is then the third of the four. This will happen once next autumn and after that in 2013, but didn't happen in 2009.
But the 'two-in-a-month' has attained wide currency. See also
here if you're interested.
Not really of any great significance, at least not as far as I'm concerned...