Habari has a policy that themes and plugins do not include links to designers' and developers' sites. This policy is one that hopes to prevent spam, linkfarm, or other links that make your Habari site an income source for someone else without your approval. However, I feel that one of the major rewards of Open Source development is the "Hey! This is awesome! Thanks." you get when you do good work. To that end, I've made the "Credit Due" plugin for Habari. What it does is gather the author information from the active theme, and any active plugins on a Habari site and makes them available for display within your theme. You can see it in action in my sidebar under "Credits".
Let me know what you think!