I have been building Joomla sites for about 4 years, and have used a lot of extensions in that time. You quickly get a feeling for the good ones and not so good. Although CB isn't perfect ( I think too many options are hidden away inside other options etc, and the interface is perhaps a little dull, plus there are huge numbers of plugins etc to install ), I have found it to be stable, reliable and enormously powerful. You really can get this software to do what you want it to, as long as you take the time to read the documentation and work through the various options properly.
I noticed a couple of reviews complaining about paying for the add-ons/priority support. How can anyone expect an extension as huge and comprehensive as Community Builder to thrive without a proper revenue stream? Practically all the good extensions out there now are commercial ones. Programmers have to eat, just like everyone else! At least you get a chance to try out the main component, which is free, before paying for any of the commercial extras, most of which add really valuable functionality to what is, in my view, a first class extension.