Google built their empire on contextual advertising; ie, anyone can have an advert up in Gmail, Google searches, etc, based upon similar content you search for or read about.
But sometimes you get... Well... Just take a look for yourselves (click for large size):
Umm... Ok, let's read it again...
Nullify Black Magic
Okay, an interesting title, wonder what this ad is all about?
Expert Indian Vedic Rituals
Ah great, just the sort of service I was looking for and couldn't find in my local yellow pages...
Remove all sort of Evil Effect
Yeah, sure sure... Can you prove it?
500%! That means it's not just one hundred percent true, not two hundred percent true, no, not even three hundred percent. Nope, you've got a FULL FIVE HUNDRED PERCENT. Holy crap, now you've definitely got me convinced that this thing is legit! Where do I sign up ?