A while ago I blogged about some of the internationalization and localization changes in 4.0. One of the things I mentioned is a "Visual Language Editor" which allows you to quickly change any of the verbiage used throughout the suite just by clicking on a word of phrase.
Not only is the really useful for those who want to translate the IPS Community Suite into another language, it can also be used to easily change words and phrases as you like (for example if you want a link to say "Register" rather than "Sign up") - it can even be used to rename forums, categories, etc.
Before I couldn't show you it in action as we weren't quite ready to show the front-end interface but now here's a video of the feature in action:
By Mark