We just did in January for our trip in May. They waived the service fee since we were using it for the first time.
The only problem we had was booking for five. We booked four on the first purchase and then did another purchase for the fifth person. Unfortunately when the SUBMIT button was hit, Orbitz said there were no more seats available for those flights. I WANTED TO DIE! I could not believe it. I called their 1-800 number to cancel the first order; they would have done that for us. The person I was talking to tried on her end to get the flight and she was able to and she purchased that fifth ticket for us via phone. Everything came back confirmed via e-mail the next day.
I called United directly that afternoon after booking and we were on their itenerary. They put all of us together for seats via phone.
I understand Orbitz is owned by some of the big airlines; I have read positive comments here about it. I would use them again if I find good airfare through them.
OOPS! You replied while I was. Can't answer your second question.