How Good is Gmail's Spam Filter?

juglugs asks: "I've been using Gmail since the first round of invites on Blogger. Tonight I received my very first spam email. It was one of the ones offering me some product (I didn't read it too much) that would increase my manhood. It didn't trouble me too much as I just had to hit the 'Report Spam' button and off it went. But how good is their spam filter? Does anyone else get much spam? Why didn't this get recognized as spam - it had all the usual 'keywords' that you'd normally associate with it."