We've used UBBthreads for several years now - we had been using WebBBS prior to that. We did investigate other forums, such as PHP-BB, and VBulletin, but we kept coming back this UBB, and eventually bought it.
When we changed to UBB, our users thought they were in heaven. It's always been easy for our users, and they love the features. One of the main things we like about it (as owners), is how flexible and customizable UBB is, if we want to add to the already great list of features.
Another thing that is the best, is the level of support. If I have a question, it gets answered almost immediately via the forums. We've also had experience of the online support, and it was not only fast - it was excellent. Rick will stay with you until the problem is totally fixed. Communication is top-notch.
7.x is a great version. I work for a software company, so I completely understand how difficult it is to make everyone happy with new features - but it's obvious that 7.x was the product of listening to customer feedback and suggestions.
And the UBB community is the BEST. Very friendly - and a lot of fun too. Well done to everyone involved - I love UBB!