Anecdotally gmail has been doing a miserable job filtering spam for the last 5 months or so. For me it used to be pretty bulletproof - one of its best features.
Now I get something from McAffee Pratners(sic) every other day warning my computer is about to expire. Back in May I kept winning things from Home Depot and Lowes; and gmail would categorize it as "forums".
No idea if its related, just odd.