My experience has been horrible. I won't go into details because I can't really remember them. But, I booked flights about 4 times and every time involved a major adventure to straighten out the mess PTO made.

One example I do remember: I went through the entire process to the purchase step. I was booking an e-ticket. The purchase step failed with the following error:

Unable to verify airfare and rules.
Please contact your support desk to validate this reservation.

At that point I just gave up and rebooked the ticket through a more reliable channel. A week later, I received, by mail, paper tickets for the "failed" PTO booking!

I will never use PTO to book a flight again.