In my experience, United does a great job trying to accommodate flyers with alternatives when a cancellation or schedule change causes problems, or refunding the fare if requested, especially compared to Continental. With Continental, it has always been a tremendous struggle (they'll refuse to book outside of the original fare class, refuse to change destinations to reasonable alternatives, refuse to book on an airline outside of Continental, even with other *A flights available, etc). More than once I've had to talk to half a dozen phone agents before I got a quarter-way acceptable solution on CO. This has always been one of the biggest complaints on the Continental board.

If you think things are bad with United, wait until the they fully merge and adopt the CO mentality!

As an aside, it is unreasonable to hold United responsible for the fact you are missing an onward connection on a different ticket. Missing the connection and having no option save buying another ticket is the risk you run when you do this. If that risk is unacceptable, buy a single ticket and then you can hold UA responsible.

Edited to add:

If they cancelled idriveuride's outbound, however, and could not get him/her to Hong Kong in a timely fashion, they should have refunded the entire ticket. I don't know the United CoC well but I'd be surprised if that is not in there.