Working my way around in SharePoint 2013 Preview bit by bit, I started by scanning through the settings of a site and site collection. There are some quite nice enhancements, here some examples of my favorite ones:

It's the former themes. I didn't really like the themes before. As for these, I haven't formed an opinion quite yet. At least there are quite many of them available and they seem more useful than before.

Plus the modification of the selected theme is easier and more userfriendly:

Design Manager (Site Look and feel, Publishing sites only)
This is a topic for a complete blog post in itself, or several. But I wanted to mention it here anyway. The new way of creating and managind branding and UI assets for sites, packaging them and importing them as well.



Site / Site collection app permissions (Site Permissions / Site Collection Administration)


Popularity and Search Reports (Site Collection Administration)




Site Closure and Deletion (Site Administration)
You can add policies for site deletion, e.g. archiving, that can then be used when a site is deleted. Also, the site is trimmed from aggregated places.