I used to use the bike racks on the bus in the Denver area all the time. I was kind of nervous about getting my bike on the first time, but discovered that the main transit stations had a practice bike rack complete with a tutorial. The long distance commuter buses also allowed cyclists to stow their bikes in the luggage compartment under the bus if the racks were full (there was never any actual luggage down there, as it was a commuter bus.)

The buses where I live now all seem to have bike racks on them as well. Much like the bus, they don't seem to get a lot of action.