I've seen quite a few webpages that use obtrusive advertising techniques such as this:
How can the signup form be blocked? I found using Adblock plus the form can be blocked, then the grayed out background can be blocked, but then the scroll bar on the side is no longer there.
It's like Adblock plus just stopped working. Here's another site that has ads that aren't being blocked http://walrusmagazine.com/articles/2010.09-environment-a-10-percent-world
Here's another example (takes some time for ad to load) http://www.howtogeek.com/121267/11-ways-to-make-your-lastpass-account-even-more-secure/
Yet another example of ads that aren't being blocked.