Nero Digital has some .mp4 downloadable trailers to illustrate MPEG-4 compression over at their site. They have a player that you can download as well, called Nero Show Time. The company has developed codecs that are MPEG-4 compliant which should provide at least a 30% better compression rate than MPEG-2 standard files. Check your graphics card for support as the largest file is a 1920 x 1072 resolution. I guess we really don't need those other 8 horizontal lines of 1080i!
Keep in mind that to free up bandwidth and add potentially more channels, the two biggies in the satellite TV market, DirecTV and Dish Network, have announced a move from MPEG-2 to MPEG-4. Detailed plans haven't been announced yet, but sketchy communications indicate the transition to begin in late 2005 or early 2006. I'll keep an eye out for some videos that are available in both MPEG-2 and MPEG-4 so we can get a comparison of quality and file size.