This would be good to have.
I started working on a perl script to do this as I am not very good with php.
I already have a client area written in perl where the customers log in and place orders and see billing infromation... The perl script calls on the osticket mySQL DB and searches for any tickets with the users email as a match then it spits out all the previous tickets - but right now it's beta... it just spits out the raw data and does not let them re-open the ticket or anything like that... it's just so they can log in and see the replies (In case they missed the reply email) ... and also to see the previous answers to any questions they have. Our staff can review this as well so we can easily look back at previous support for each client.
A system that would let them log in, open and close cases, etc.. would be amazing.
Our webhosting company has that and it works very well. They do not use any email support (Only tickets that they refer to as Open and Closed "Cases") it's a very clean set up. I am slowly trying to modify osticket to act the same way but my PHP work sucks and involves a open reference manual at this time.