The topic came up before. I'm pretty sure it's based on the content of the thread more than anything. Either way, small price to pay for free use of this website.
e-mail works the same way, they sell addresses based on what you have searched for or recentely purchased, of course most of it ends up in your spam folder.Google has it all figured out.
My antivirus wouldn't load the page due to the ads on the right. Stated there could be malicious code in the ads which in short translates to cookies being used to track your web activity
Not a huge deal.. but that is why the ads correspond to your searches