When I've had to walk distances with my scope, I've use a Manfrotto shoulder-strap/sling set-up.  It's reasonably comfortable, there's no dangling/swinging tripod legs involved, and it's a lot cheaper.  Downside is that the scope still hangs down so you have to be mindful of it, and it probably takes an extra minute to put it on or off.  Also note that I have a fairly small tripod--it might not work as well with one of the monsters.  The name seems to have changed, but Eagle Optics has a product called the Manfrotto 401N that looks like it is probably the current version of what I have.  I would guess there are other brands out there of this sort, too.

Eagle Optics also has something called the Duckbill that seems similar to the harness Kurt initially asked about.  I haven't tried these, but it seems to me these make the most sense if you're birding alone and walking across a large wide-open space.  I have a hard time seeing how it would work in vegetated trail conditions or with other birders around (I agree kneecapping seems likely).  You might reduce the problems by completely collapsing the tripod, but then you seem to lose the easy set-up and take-down that I assume is supposed to be the advantage of these things.

Jason Waanders
NW DC
jwaandersATstarpower.net