At a friend's university, some of the machines have an application called _STOPZILLA_ that caused me to sit there for about 5 minutes, wondering why a link here on WebmasterWorld wasn't opening up.
That machine and the others around it all seemed to have the application installed. We were in a library, and I was using machine 300-something. So, I'm assuming this thing was fairly popular.
Later on, I went to a few other sites as well - and had the same problem. You can click a link (intended to be a target="_blank") and nothing happens. I know that it interfered with these types of links, because I owned the sites with the targets set as such.
Another thing that I've gotten from members of a forum I run, are emails saying "I clicked and clicked link X, and nothing happened!" Funny for me since those forums worked fine for the past 3 years. Upon asking, they've all recalled that they've installed or seen applications like this running.
Progressing this back towards the original topic -- does anyone have information on how the introduction of new windows affects usability, conversions, etc.?