I have and have used the GlideCam V8 with my Canon XL1. Like Rob says, it can and does tire you out after awhile. I have the complete system - vest, articulated arm & support, and the stabilizer assembly. I've used the system both ways, with the complete vest/arm/stabilizer, and with only the stabilizer. It does GREAT for planned shots, or for a series of nice, smooth floating shots during any kind of event.
I doubt that "running" along with it, like the SteadiCam guys are seen doing in movies, is going to work out very well.
I am too old and too puny and too slow to use this system much anymore. I spent about $3K for it back when. It has done me well with static events, when I've wanted to get smooth passby shots of the attending crowd, or move up and in on certain elements of the event, or simply sit in a chair and hold it for smooth movements side-to-side.
I'd hoped it would help me when I purchased it because my shooting arm and shoulder were beginning to hurt a lot after extended shoots. It did, after a fashion, but still fatigued me though it didn't cause my arm and shoulder to hurt as bad, but it began to bother my back somewhat - I'm simply just NOT strong enough.
First $800, plus shipping, gets it.