We are currently using it at my company and my team administers it. It works like many other defect tracking systems (it is work flow driven).
The system has a degree of user configurability which is nice as long as you don't get carried away with it. Segue is in the process of trying to improve this product and are moving in the right direction.
I would give it about 7 out of 10 for defect tracking (I have used and administered PVCs Tracker and StarTeam).