This should be moved to the Travel sub-forum.
I'm 1K on United. Within the United States, I think their service is comparable to the other non-low-cost carriers operating domestically. (eg US Airways, Delta, American).
United has frequent cross-country non-stops and manageable hubs in SF, Denver, Chicago and the NYC area (JFK I think is a hub) so that could be a key decision factor to select them or not. Same with price. Unless you get a good sale, their prices seem slightly higher than some of the other carriers.