I've got the Yamaha VX2500 and it does a great job mapping 5.1 into 7.1! Any surround sound is more defined and envelops the room better. I've noticed that it definitely helps a lot when there's echo in the movies (like when bullets strike). It's not like a night and day difference but it definitely adds more realism to the movie. We were watching Indiana Jones and the Temple of Doom and my wife got startled by noises coming from behind, also she thought there was some water dripping behind us too. It's amazing how much realism those effects can add.
I also enjoy using the receiver's ability to map stereo into 7.1. I enjoy watching tv shows on DVD (like Stargate SG! or Battlestar Galactica) and they usually are in stereo but the receiver does a great job mapping it into 7.1 and it's pretty accurate in placing sounds.
