I was just looking at my email account with its 728x90 wide ad smack in the middle of the screen, well slightly above center but that's beside the point.

What got my attention was that it was an ad about a widgets site and I had just visited that widget site. Curious I cleared cookies etc and visited one of my sites and then checked my email again, sure enough the ad is now based on my sites topic. A 3rd try to a bank website and again, a loan offer. A 4th time to my fantasy ball team and the offer this time was tickets to an upcoming game. A 5th time to a car dealership and yet again the next ad is a vehicle ad.

It's uncanny if it's coincidence but I highly doubt it is. Is this kind of spying for profit legal? And if so... where can I get such speedy ad hosting that can determine what an ad should be based on referrer and serve it within a nano second.