Two things, one, if you buy them online they are only good for about three days after purchase. You have to call GAT to tell them when the time frame of your trip is to make them valid at that time. I would actually order over the phone instead of online. We purchased some online and added a few more over the phone. The ones purchased over the phone were in the Disney system. The online ones were not. The CM called GAT and they straightened it out. But it did take about 10-15 minutes to do so.
Second, we got into Anaheim after the guest service window closed as the park closed at 8:00 that evening. We were staying at Desert Inn and they cannot print the GAT vouchers. We had PS at Storytellers at 7:30 the next morning and Guest Services didn't open until 9:00 that morning. So we went to the front desk at GCH and they were able to print all of our vouchers AND Park Hoppers. It was really easy! The CM at GCH said that the Desert Inn could have printed them since they are a Good Neighbor Hotel but they are not online with GAT.
We would definately use them again for our vouchers!! Have a great trip!