BuddyPress.org

cc @boonebgorges what’s the timeline for compatibility with current BP?

And, for what it’s worth, the idea of a “component” is not one with clear demarcations. Both you and @modemlooper suggest some useful criteria:
– if your plugin creates new data objects, it’s probably a component
– if your plugin needs to have a top-level directory, it’s probably a component (and, in this case, a special kind of component called a “root” component.

In BP 1.5, the idea of a “component” has a little bit more technical fleshing-out due to the BP_Component base class. A quick look at that class and its more important methods (setup_globals(), setup_nav()) will give you sense of when it’s useful to think of a plugin as a component. But again, there are no hard-and-fast rules.

In general, when in doubt, I would suggest using the BP_Component class. Sometimes your component won’t need some parts of the component infrastructure – sounds to me like your “up vote” plugin doesn’t need dedicated navigation items, for instance – but in that case, you can just leave those methods out. Using the BP_Component class just makes your life a bit easier by hooking you into the BP load order in the appropriate places.