1. Change the color of the "comment" link please (or use a button). At first, I wondered why all those messages had the word "comment" in them :) And then I tried to respond to this message and searched for the "comment" button and I was enlightened!
2. Document before writing new features :) I'm really curious to know what the "showdead" option is (I don't want to try it because the name is so scary).
3. A URL (or free text) field in the profile.
4. Keep it simple. I think it's nearly perfect as it is (the sign-in form is great).
5. We want to see Arc and the source code of this app :)