I have been in the web design business for a few years now. Everytime I wanted to track support issues for my clients I used a simple form that would email me their request. Now that my business has grown I needed a professional solution - and found RSTickets! Pro. This is by far the best support system I have ever encountered (and I did use a few stand-alone scripts but they didn't quite feel right). With the "Cron Email Parser Plugin" I can discuss issues with my customers by email while still keeping these records in my Joomla! database, it's simply amazing! No flaws I can point out because I haven't dealt with any issues yet (I'm using REV 3, which is the latest as of now).
Highly recommended! Worth the small price!