A few tips for ning administrators:
1. Public or private? If you hesitate between a public ning (attracts new members online) or a private ning (makes it easier for members to share information that they don't want to be public) you have the option to choose for a public homepage and a private rest of the site. When people who are not a member click on other tabs they are asked to become a member or log in. You can change this lateron too through 'manage'.
2. Integration of external pages You can use external pages and make them a tab in your ning. A ning for libarians (betabiep) decided to create a netvibes page about the darwin year. They added this page as library page in their ning site. Since ning does not offer a wiki or document sharing functionality, you could add an external wiki page with lists of documents or links.
3. Language You can select the language of your preference for all navigation. If you go to manage click on languages, you can already choose from 25 languages, or you can work on translations and add a new language.
4. Hosting on your own domain. If you pay 4.95 US $ per month, you can host it on your own domain.
5. Email subscriptions. Not everyone may use RSS feeds. At the Forum bottom of the page there is a possibility to warn you by mail when new discussions are started. Depending on the topic, you can then decide for which discussion you would like to receive a notification in the mail of new contributions. This system works very well (for email based workers like me!). You can use feedblitz (or similar service perhaps too) to offer an email subscription to updates too. See in the left corner of the africanpath ning (picture).
6. Chat option. Though I ticked the chat function, I don't really see it working. What you can do is integrate an external chat function like meebo and embed it in the ning site. This is something I first saw in the ning about Worldwide story work but now I don't see it there? Update: (thanks to Demetri) if you tick the chat function at the bottom of the page you can see how many people are online. If you click on it, you get a chat functionality. Apparently the chat function may slow down your pages.
Do you have more tips to customize a ning site to your needs?