It’s always sad letting go of a domain. I love owning domains — each one represents a fresh slate, a new incarnation of my personality. Empty ground to build something exciting.
Dear8ball.com housed a fun little robot application I worked on for a while. I plugged it into twitter via a jabber bot so that you could simply reference it: @dear8ball ___(question)____ and it would grant you a magic 8 ball reply. It worked pretty well! It was a great project that I got 85% through, ran into a little technical difficulty, and then more or less lost interest. It happens.
And that’s a good thing — I wish it would happen more often. Every good idea does not merit implementation. Incidentally, it looks like someone else did work on a similar project (though that looks to have gone extinct now too).
In my pairing of domains, I recently gave away listmaker.org, and have let a few others expire as well. A little focus never hurt nobody.