I just enabled Public Tickets and I like what's there but I can see some additional features that would be nice. The first would be some sort of notification of a new ticket. This could apply to all projects though. That way a project manager could automatically get notified when new tickets are created without having to be subscribed to the tickets. If they see one that catches their interest, they can then subscribe to it. I understand you've provided RSS feeds for this but e-mail is just more convenient. Plus I'm going to assume that at some point down the road (it may be a while) you're going to allow people to interact with aC via e-mail. So a new ticket could come in to my inbox and I can immediately reply if I need more information.

This leads into my second request. The person that submits the public ticket is listed with a link to their e-mail address but they are not subscribed to the ticket because they don't have an account. My suggestion here would be to allow subscriptions without having an account or the ability to auto-create accounts with default permissions so they could then be auto-subscribed to the ticket. Personally I like the second option so the user can then login to the site at a later time to easily check on the status of all their open tickets.