I completely agree. There are so many fantastic products out there; forums, content management systems, ecommerce systems, and so on, but so few of them have a friendly, well-moderated community. Part of me thinks that XenForo has this because everybody is genuinely excited about the product, because let's be honest, content management systems and ecommerce systems have progressed miles beyond the last innovative forum*. Another part of me thinks XenForo has this because we are here at the beginning. Three years down, with XenForo being a successful and popular product, will the community feel the same for a new user (and an old user, for that matter)? I hope so.
XenForo has already become one of my "check regularly" bookmarks that I come back to when I'm supposed to be working.
* Although now is an interesting time, what with the release of Vanilla 2, 'upcoming' changes to bbPress, phpBB3 3.1 and Justin Tadlock developing a WordPress forum plugin using custom post types. Still XenForo has completely won me over!