we use
h2desk for our support system. i turned off vbulletins contact us feature and manually replaced the contact us links with links to the support system. we made no attempt to integrate the tickets into the forums. you dont need a separate account to submit a ticket but you can create one if you want. it works good, it makes managing users problems much easier. i highly recomend using some kind of advanced support system if you have more than 10 emails a day related to support matters.