Deseretbook.com, who uses ACS and AOLserver, has implemented such system about a year and a half ago (if memory serves right). They presented about it in our LUG back when it was in beta.
They use a pretty clever system that lets the use print the ticket right from his browser. The ticket has a bar code, and at the venue entrance, laptops equipped with bar code readers scan the ticket. You are free to print the tickets as many times as you want and give it to your friends, but whoever gets to the venue first will be the one to get in 😊
You can see it in action at http://deseretbook.com/tickets/.
The deseretbook.com staff also wrote an ecommerce system for ACS 4.2 (Oracle), which I've asked them to open source, and apparently management said yes, but I haven't heard back from Michael (Cleverly, who works at deseretbook.com) about it.
It would be nice to see the code for their ticket system open sourced as well. It probably does what you're looking for and more.
/me waits for Michael to chime in 😊
