For grip, the
UPstrap is hard to beat. You put it on your shoulder, and it just doesn't move. Period. However, the attachment mechanism is a royal pain. I'd rather have a modular system that had small, in-line pincher closures (not sure what they're actually called) on pigtails unobtrusive enough that I could leave permanently attached to the camera and take the strap off when I didn't want it.
The rubber pad on the SLR model is huge. I generally carry cameras either straight on a shoulder or across my chest, not hanging directly off the back of my neck. However, when I'm juggling multiple cameras, I sometimes do go straight off my neck, and the massive pad is really annoying. (It may be that the optimal solution for two camera event/PJ set-ups is a chest harness that can hang a cam off of each collarbone area, I don't know.)
The other problem is that because the grippy part is small and centered at the top of the strap arc, it can be annoying if you're bending down a lot to shoot macro or other things on the ground. You have to reposition the grippy part, and it needs to be at different points for standing and squatting/kneeling, so you have to re-adjust every time you make the transition.
I think the answer to that is to keep the UPstrap's nubbed soft rubber surface, but make it thinner and find a durable way to adhere it to the underside of the strap material. You'd eliminate the bulk and could cover more of the strap with it, which would eliminate the need to "aim" the grip surface.
The one benefit that the heavy pad provides is that it's heavy, so it pulls the strap down and keeps it fairly out of the way when you're shooting with it attached but aren't wearing it, as well as on tripods. (It tends to not pile up on the the camera the way lighter straps do.)
I dislike neoprene because it's elastic. Stretching downward when a foot hits the ground when I'm walking is not a problem, but the rebound is: it creates a moment when strap isn't bearing the weight of the camera, which allows it to move around on my shoulder. If I wanted to babysit it all the time, I'd just carry it in my hand(s) or bag. I expect both actual security and a feeling of security from camera support that elastic materials don't provide (for me).
The adjustment lock on Crumpler messenger-style bags is pretty good, but I think some experimentation might be needed to make sure that it wouldn't be accidentally unlocked by an elbow in camera-carrying positions.
I'm a bit of a physical interface/design geek and would be happy to discuss this more if you want to.