Sidebar can be customized by adding a plain text in db/config/sidebar/.

The format can be in markdown, rst, html and tex. All determined by file extensions.

Then edit this line in db/config/site.txt

sidebar = Blogroll.md

The base filename will be used as a header for your sidebar item.

Since you can embed any html snippets, I assume putting a twitter badge or some flickr photos are relatively easy.