This is yet another interesting thread, and I know my comment will be off of Malcolm's topic, but since the topic of a shoulder-mount scope was raised, I'll mention the set up I have, for what it's worth.
When I know I'm going to use a scope intermittently, or a great distance from the car, I carry a Nikon Sky and Earth 60mm (I believe they're also called RAII) with a 20x eyepiece. The scope is mounted on a BushHawk shoulder pod, and I can sling the whole kit over my shoulder or strap it to a back pack.
The 20X eyepiece yields a pretty nice view, and with practice, I can hold it quite steady. It works nicely for hawk watching. It also travels nicely - it will go with me to Arizona in May, even thought the security inspectors at the airport do look a bit askance at it!
The whole set-up cost me just under $300 US. The big Nikon travels with me more and more, now that I lug it around on a Tri-pack, but for real light-weight travel the little scope and a shoulder pod can't be beat. It's also nice to have a back-up or second scope when I'm leading bird trips here in Maryland - I can loan it to the "telescopically-disadvantage!"
Scott Crabtree