No, this isn't a rant on how Google's spam filter works, it's an observation on how two different technologies can come together in unexpected ways.
One technology is Google Mail's spam filter. Nothing new about that, and Google's spam filter probably isn't any better or worse than any other. It does tend to put most spam into a folder labeled, appropriately enough, Spam (okay, it's not a folder it's a label, but you get the idea).
The other technology is Google's context sensitive advertising, which displays ads relevant to the text of the message you're reading. Normally, these ads display only when you're actually viewing a message, but recently Google Mail started displaying some ads, along with the headlines of RSS feeds, in a banner on all the pages. So you can get context sensitive ads based on the titles of messages, or even based on the labels you're viewing.
Lately, every time I look at what's in my Spam label (because sometimes it does put real messages in there), I'm treated to ads for "spam casserole", "spam primavera", "spam roast", etc.
So if you're ever in the mood for a good spam recipe, get a Google Mail account and take a look in the spam folder.