I've taken the USAir shuttle DCA-BOS a couple of times this month. They do seating on day of flight, so you get to pick your seat when you show up. They don't pre-board by status on the shuttle ... plus most shuttle flights are one-class. I can't comment on most of your questions.

However, yesterday I signed up for standby on an earlier flight to DCA. The gate agent said the flight was packed and I'd be lucky to get on, unless I was "Preferred Gold" (their 1K level), we're only code sharing on flights with UA so their status doesn't matter, blah blah blah.

She actually caved and pulled up the standby list and HAH! I was the first person on the list of 22 pax. She was surprised to find out that the Elite levels carried over. So she gave in and printed me out a boarding pass for seat "2A". I'm an aisle person but I figured now is not the time to be picky so I just got on the plane. Very very happy to find out that this particular shuttle flight was 2-class and she had upgraded me gratis.

So, I'm kind of hip on US at the moment. Plus they have better snacks - an actual choice of name brand pretzels, cookies & chips. (Not those mystery UA snack/party mixes)