I went to the Temecula and first LA shows, and the ticket process couldn't have gone more smoothly. I was quite early both times, but my tickets were at will call. On the email I received from MK.com, it said I'd have to have the credit card with which I bought the tickets, plus a photo ID, but both places only asked for the photo ID.
At LA, they had a table set up outside for MK.com buyers, but since I was there quite early, I got mine at the regular will-call window. I did see people getting their tickets at the outside table, which was around the corner from the main entrance.