Activity streams are great !
They could get better with the introduction of hierarchical activity streams

The way that most JIRA instances get configured are (from what I know)

Projects -> (Versions, Components) -> Parent Issues -> Subtask issues -> (Worklog, Commits, Comments & Edits)

For instance if I'm looking at a certain parent issue (such as a story), I would like to see all activity related to that issue, including the subtasks.

If I'm looking at a version (or component) I'm interested in what has happened with that version.
Currently the activity stream either shows to much (like in the activity stream gadget) or too little (like in the activity stream panel of an issue).

It might be an idea to base the activity stream on a filter