My b2evolution Version: Not Entered
I'm pretty sure this is not done before. What I did was made it so that if a visitor clicks on a category name they will get results across multiple blogs that match exactly that category name. One needs an aggregator blog for this to happen, but then it won't matter if the visitor is on the aggregator blog or not.
In my case a musician has been a member of many bands. Each band is a blog. Each album is either Available or Sold Out (categories). All posts in band-blogs are aggregated into both an online store blog and a blog used to post regular blog posts. So when a visitor clicks on "Available" they will get a list of all available albums from any band-blog.
The one thing I don't have quite right is that they don't end up in the aggregator blog even though they get the aggregator behavior. So like blogs 1 and 2 are aggregators. If you click "Available" on an album in blog 6 the URL and skin indicate that you are in blog 6 but you get all the posts as if you were in blog 2.
So should I write up this improvement or does no one else find value in it?
2.4.7 by the way. Right now the list of bugs in the "stable" version of v3 is longer than my list of known improvements it'll need because improvements from the teeming masses are generally not part of any release. So I'm gonna wait even more for a "really stable and actually tested" release before cleaning up v3.
Update: this project is dead. It worked, but it killed getting regular normal category links. Oh well.