I disabled it for 2 seconds. I reloaded twice and saw 1 advert about some dating site and a charming innocent imvu advert
http://i.imgur.com/7j2shyP.png
This is why I keep them off.
It also actually slows down loading of pages for me rather noticeably (i live in a really crappy internet area js).
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You can also disable customised adverts iirc.

