I'm just going to get each of my kids their own separate entertainment kit when they're old enough. Things like the PSP that play movies, games, etc. That way there's no fighting over what to watch or what to play, it doesn't matter which vehicle we take on our road trip, they'll work on airplanes, and (most importantly) I can use it when im on travel for work.

In other words, I think in-car DVD/Entertainment systems are past their time... it's a lot of money and effort for a "good" system, but then its still only useful in that particular vehicle. Portable devices are much better and more powerful.