In his post about high def communications, Rich Tehrani lays out a pretty good argument about the need for High Definition in communications.
In my business we've been using HD audio conferencing from HighDef Conferencing and the comments from my team members and clients is consistent about the experience. The calls are simply better. As a result people hear each other better, less time is wasted asking someone to "repeat what they said" and the parties to the call are more engaged.
With HD Video via Skype the same effect rings true when having a video call. The impact is dramatic. You feel like the person is there with you, not some crappy picture like you see with one of the IM based video services. When I use my Agent web cam with SightSpeed I get an even more immersive feeling of closeness to the folks on the other side of the screen. Have them use the same web cam and wow, it's like something that can only be experienced (note a new version is due in February.)
To make this work best though we need more reliable bandwidth, more stable routers and better processors. You won't be doing HD video over a netbook that soon, but you can with an Apple Mac Book Pro and an add on Webcam from Agent or Logitech and your going to see things far better.
For audio we need things like better echo cancellation, background noise reduction and smarter voice processing in the audio engines.
Put all that together and HD means the idea of being "virtually there" is really true.