Actually one of the primary examples would be TextEdit, which can share (via services) it's ability to spell check, or use (via services) Grab to place images. Ideally you could have a ton of small apps that each did a couple things very well that would replace a hand full of very large (expensive) apps. You would only get the apps that gave you the features you wanted, so the system would be customized for you (instead of the general public).
Carbon is very new and it's apps are not able to use services yet, but Apple plans on them being able to in the near future (which is why the menu is there now).