The idea is to have a single RSS feed which users can subscribe to, which could contain events for changes made in a project in the recent past. The type of events (comments, worklog entries, issue created events) would need to be configurable. One should also be able to define the RSS in terms of a search-derived issue list, rather than a hardcoded project.

See this thread:

http://forums.atlassian.com/thread.jspa?messageID=257222381&#257222381