Yes, had problems a few days ago. At first I couldn't get the reservation screen. Once I did, everything worked fine through the booking process and entering payment information. On the final mouse click to confirm all information, I received an error screen.

I called reservations and was transferred to web support. The agent had a heavy accent and was nearly unintelligible. After some struggles he was able to replicate the booking and price. United clearly has some IT bugs to work out.

Having to go through this process was annoying but only a minor inconvenience. The only thing that really aggravated me (aside from the difficulty in communication) was the agent's volunteering to waive the telephone booking fee as a courtesy. Really? The website bombs, forcing me to take the time to resolve the matter on the phone, and United is doing me a favor by not adding a gratuitous fee?