In the past few months, and especially since the 7th Edition come out, I have yet to see an army with more than one Daemon Prince lose. And all the games I've either played in or watched, the contest is not even close, the daemon Prince Army just slaughters the opposition. All the enhancements one can give the Princes seem to make there nearly impossible to beat; they can swoop in and go about destroying units. Heck, in many of the games, the most damage to the Prince army is caused by perils of the warp.
What does it take to defeat these guys? Do you have to have a list specifically tailored to beat them? What would Space Marines or IG have to do to beat them? I'm to the point to tell my opponents that if they are going to bring more than one Daemon Princes that they have won and I'll just stay home.