I've been working with Joomla! for about 2 years now (Been in IT development for about 20 years) and have tried countless extensions for the Joomla! platform. This is a *must* extension to have on your Joomla! website. This extension will give you so much flexibility. Joomla! is a great content management system and Community Builder will give you the social network edge to your website and I've never had to use Community builder forums once in 2 the last 2 years. Simple to install and administer and very stable with Joomla! 1.5 (make sure you have legacy mode on). Can't emphasise how important this extension is to you website.
Thank you for your very nice review. As general information update since this review, Community Builder 1.2 Stable is released and runs native on Joomla 1.5, Joomla 1.0, and even on Mambo 4.5.x and 4.6.x. Also CB Team plugins are now available universally native. So the legacy in Joomla 1.5 is now needed only if you have non-native third-party CB plugins.