40-50 was my reccomendation with XC tires. anything beefier, like freeride, downhill, or even high volume(2.3+) can be run as low as he reccomends. also depends on rider weight and smoothness.
I used to run 25 there with XC tires on the old full-rigid. I really didn't go very fast back then though. Having said that I wouldn't really recommend it.
1. I usually run 40psi, but then again I hate changing flats.
2. Just ask if you can pet the dog, and ask her a couple of questions about her dog. If her body language suggests she may be interested move on to regular small talk, otherwise keep on riding.