I always thought the What's New link being the first in line of ... What's New, Mark All Forums Read, Watched Threads was somehow not quite right. Also I remember Kier posting the same somewhere (can not find it back... where is that XF Bookmark function?) . Can not explain really why it felt that way (maybe because in vBulletin it has a more prominent place more to the right, don't know), but now they've moved it to the right! .
I keep almost hitting "Mark all forums read" (because I'm used to that spot being "New posts" on vB), which I don't want to do since I haven't come even close to reading everything and still want to! Luckily, there's another confirmation screen beforehand that kept me from doing so--thank goodness for that.
There were a *lot* of subtle changes in the navbar, before the "forums" drop down menu needed to be used much of the time, and that took some reasonably well controlled mouse movement. Now the "watched threads" and "Whats New" are big buttons that stay in the same place every time. Much much quicker!
No more clutter in the watched threads view either, such as setting avatars, privacy details, email, etc.
No. It depends on the way a certain function is used. It doesn't always have to fit (like here -screenshot included) in the 'most used comes first in line'. This 'What's New' is a perfect example of that.
It is not that easy to create a good solid UI, but really XenForo nailed it almost perfectly in the whole package. I keep being impressed.