In response to Matt S. video at vimeo.com/10696025
Matt did a good run through of the Glidecam 2000 Pro. I used that model a few times, but mentioned that I opted for the HD version mainly because of the 'Fine tuning' adjustment knobs that are not available on the older 'Pro' models. Other than that, it's pretty similar in functionality.
Here's a video of what those knobs look like and how they work. Much different than the older version shown in Matt's video, but it's probably double the price just for those knobs. You make the decision on what you might want to spend.