Would be nicer if it was able to fully merge with Wordpress/Joomla/Drupal which the licenses seem to restrict, but that's purely selfish on my part and with my personal wants aside, yes I am perfectly in agreement with the 'principles and philosophies'.
EDIT: I only mention those because their "philosophy" is freedom and thus I thought it applied to here. It wasn't a pitch for a feature or anything. It's relevant, I promise.
I think XF is on the right track and I always loved simplicity (with a comprehensive front - and backend functionality), I use the same principle on our site. One thing: sometimes the principle of making everything simple and clean can go to far. For example the latest layout changes on YouTube made it worse for me. I do not like the fact that almost everything is hidden and you have to hover to see important content. Same thing has happened on Google Images. I think these changes were a mistake and do not help usability.
It is such a complete breath of fresh air. I can come up with a fair amount of suggestions to make the existing functionality a little bit better in some areas, but I could never have created/thought of the existing functionality in the first place and the underlying fundamentals/vision myself like this. 95% of what has been shown to us in this alpha release is just... perfect and soooo well thought out from the enduser perspective. I am really impressed. And to prove to yourself how good and refreshingly innovative this UI is, just take a look now at the current biggest 'competitors' (vB, IPB) out there... I mean... the difference is suddenly sooo huge! I always found vB4's UI/UX very bad on many levels, but since XenForo saw the light... it appears to be even worse then I thought it was... (and I mean this).
A breath of fresh air it certainly is. It's quite an achievement what they're showing here, and it is obviously going to go places. I enjoy the simplicity behind the complexity of a good system. It's scoring points on all the modern itms such as progressive enhancements, user interface and user experience. To name a few.
In case of XF that's not necessarily true. A lot of visitors and new members here are just checking out the new software and most of them are (obviously) using other software ATM. You can't really speak of fanboys in such a case, yes everyone is positive about it because they know who's behind all of it, but on the other hand, these people are also known to be very critical if something is not good enough. So I think it is actually pretty representative to a more general group of administrators.