The initial web interface is still fairly basic, the back and forward buttons are handled by the browser leaving only the parent button in the apps toolbar. Home and Heart are your home dir and bookmarks respectively.
Clicking on a row allows arbitrary annotation of that file. The annotations are stored in either native kernel level Extended Attributes or RDF. A feature I find very useful is that all metadata is presented via the same interface. As you can see the "Annotation" column in the listview is showing your own description of each file. You can filter or sort on annotation just as you can on the file name.
The search page allows you to find files by their text content (full text search) and/or their metadata. As I've mentioned in the past, the metadata indexing modules include many optimizations above using the native APIs. This includes indexed lookup on certain classes of regular expressions. Many naive query evaluations using regular expressions will result in a linear time complexity. And unless you have used explicit code to handle it, you are likely to enjoy this bad performance even with very advanced indexing libraries and databases.
Tags or "emblems" etc are also handled through the same metadata interface. The tagging sidepanel offers suggestions for existing tags as you type and allows you to create new tags as you attach them to files. Removal of a tag is just a click away.
Of course, clicking a filename shows you the file itself over REST. This allows you to stream video files over REST to the Nokia n9 for example. There is partial IO support and write support so I could include a fancy text editor or image editor component in there... Unfortunately YUI 3.5.0 doesn't seem to support "selections" in the datagrid, so that nice visual feedback will have to wait for yui 3.6.0.