We might get a little insight from Google Adwords. If you run a Google ad and have a pop up on your landing page, Google will disapprove the ad because the user can't go back by hitting the back button. The back button is effectively disabled which Google defines to be a bad user experience. target="_blank" is different but Google likes for users to be able to easily return from whence they came. I would say if they take 200 factors in ranking sites and your site and another are tied after 199 factors and the other guy is not using target="_blank" than he will rank above you. It won't be a big factor but it could be the differentiator between two sites.
A simple html code that makes page open in a new window: <a href="http://www.example.com" target="_blank">Example Site</a> Code (markup):
popup blockers don't block popups that are for the same domain. external links can and will get caught.
That's a good point, and I think part of the reason for this, is because Google has almost acquired a monopoly on the search engine market. Hell, when you talk to someone about searching on the internet, most of the time people say they "googled" this, or "googled" that. People aren't even using the word search! So the scary thing is that now Google has all the power. If Google bans you from their search engines, it's almost like you've disappeared off the internet. That's a lot of power to be invested in one company, especially one who makes it's money by serving context sensitive ads (ie. spyware/adware) for it's bread and butter. Solution: Use Yahoo! Their search algorithm has improved drastically, and if you haven't used Yahoo! in awhile, I recommend you try it out for a week. The results are equal to, if not better than Google's, and you're not contributing towards a Google monopoly. Tell me again why I should use Google's search engine? Oh wait, there's no reason why I should so I don't. Feel free to rep me, but more importantly: BOYCOTT GOOGLE