I enabled this feature and noticed that it did disable the opening of popups, but it also doesn't open windows in new tabs for me. I tried to disable the option by setting the command value to "false" however that didn't work either. I've tried quitting safari after turning it on and then back off and still nothing. Now links with targets don't work for me at all. Don't run this unless you're willing to go through this glitch.

Safari 3.1 (5525.13)