My company (Mad Wombat Software) is building software that would be perfect for you. All customer mails go to a single mail address, and you can manage it from there. Every 'ticket' is owned by someone, but you can set up custom views to simulate a shared queue.

It's got a nice web front-end, but you can manage everything completely through email. We'll be going into beta shortly, and we'd be happy to set you up with an account. Contact me at dave@madwombat.com.