Yes, I have used ITN once to actually make a purchase.

I was trying to buy a ticket for a friend on a DEN-FLL fare that had already been pulled from most of the Res systems. The ones that still listed the fare wouldn't allow a 3rd person credit card to be used. ITN was the only one that still had the low fare and let me buy the ticket for someone else.

Now I don't feel QUITE so guilty for utilizing their resources several times a day to check on the availability of F seats!