I'm a total klutz, so I know what you mean. I'm pretty sure you're right about it being friction based. From what others have said, it's a pretty snug fit though, so I'm not worried about it yet. Mine should be here tomorrow or Friday--I'll post my impressions and probably some pics to that thread when it gets here.
Awesome! Yeah, please post impressions. I would be wearing mine horizontal on a police belt so a clip would be that much more important but if the HTC holds good then I might just go with it.