This week I picked up the Farseer Physics Engine, which Neil showed me a while back.  In my efforts to create an interesting data visualization experience (e.g. Connectable Lines, Radial Network Graph), I've wanted a UI that could "distribute itself" on the screen.  I wanted something that looked natural that could space itself out.  I needed the ability to introduce forces (attraction and repulsion) between UI elements.

By picking up Farseer I was able to accomplish what I wanted and created what looks like a "molecule" of UI elements:

http://www.kindohm.com/sl/molecules/molecules.htm

This may sound a little surprising - but there really isn't any interesting code to post on this! The Farseer engine takes care of everything. The UI and body/geometry logic is not much different than what Farseer already provides in its example applications and in the documentation.  Place a couple of items, join them with a linear spring.  Done.  I won't say that the UI is trivial, but like I said, there are already other examples out there. 

As for my first impressions of Farseer, I don't have any experience with other physics engines so I can't be too critical.  I found it easy enough to use and tweak to my likings, and I look forward to using it more.  I haven't come across any bugs yet with collisions or anything else.