Did spam find a way around Gmail's filters?

My Gmail account used to be virtually free of spam. Not only was I getting no spam in my Inbox, ever, but I also was pretty impressed that I received almost no spam directed to the Spam folder. In over 18 months of account activity now, I must have gotten less than 10 spam messages in my Spam folder.
The Gmail filters were just as effective as they were announced to be.

Well, those days seem to be over...
Starting about a week ago maybe, I began to receive a few messages of spam per day, sometimes only one, sometimes a few more (still <4-5 for now), steadily, every day ; this had never happened before. But what's more, most of them don't make it to the Spam folder, they just get to my Inbox, which means that they are not recognized by Gmail as spam.

I haven't seen any news or blog posts about this issue yet, but it is happening to several other people around me, and it has been happening for the past four or five days now. So I don't think I am an isolated case.
I'm wondering how many people have also noticed this trend?