If necro'ing an old thread is against the rules, please go ahead and delete, but I figured I'd add a 2013 data point.
I just called the silver line over a concern about an upcoming reservation - a tight connection in PHL going from F to A - and was left with an overall good impression. The agent answered the phone quickly, was in no rush to get me off of the phone, and helped me apply common sense to my situation instead of just reciting policies. She walked me through what I might do in terms of a flight change or a move up, and was polite (but firm) that she couldn't waive any change fees, which is fair. We basically concluded that both segments are frequently late, and that the better rationale for changing to an earlier flight was to avoid delays in getting to the west coast. The call went to NC.
For what it's worth, I've received generally good service from the main number before I was Silver as well. It was sometimes less understandable, often less personal in terms of the agent wanting to understand a situation, but usually just as polite and generally got me to my desired outcome. I think US has come a long way on its customer service at all levels. Except the lounge dragons. They are still hit or miss.