I prepurchased our tickets from the Universal website before our trip in August. We had no problems at all with the e-tickets.
I love using e-tickets because it means I can print them and stick them in the trip organizer without any delay. I have the electronic version sent to my gmail account, so I lose them, I can easily print a new copy of the ticket from anywhere. It's a bar code keyed to each person's name, so printing a new copy doesn't make much difference.