Since I have installed 4 instances of ISPconfig3, they have been working fine. I have a few web hosting accounts on preliminary trial - so far so good and running very fast.
However, I find it is a bit lacking on the backup and restoration features. I hope it can be integrated as part of the admin control panel.
Looking forward.. planing to spend sometime to understand the admin interface. I hope I can contribute to improve the UI and further make it more user-friendly. I don't aim to make is very sophisticated as most business users or subscribers are just simple users.
Also, many thanks to Till - wonder if you are one of the developers?