I have my tabbed river up a running (
http://river.mindpress.in), although it needs to be cleaned up a bit from a visual aspect. I'll try to post all the steps I had to do in order to get it running.
One thing that is now bugging me is how to add new subscriptions that I find while browsing the internet. Say I find a very interesting site that I want to follow and subscribe to in one of my rivers. By the way, each of my rivers is like a "folder" in Google Reader or a Category. So I find a site/blog that I want to follow in an appropriate River. I click on the Bookmarklet that I added to my toolbar for that specific River. The problem is it keeps going into the River of the user that I'm logged into (usually Admin). So I end up having to log out, go back to the website/blog and then click on bookmarklet again and sign in and add that feed to the River.
Seems to me that since the user param is being passed from the bookmarklet it should just add the feed to that user automatically regardless of which user I'm signed in with. I saw the Open Subs feature and that could work however I can't use it like the bookmarklet code. So a feature request is to enable those that run multiple rivers as folders/categories to use add feeds to their respective river based on the bookmarklet param "user".
Thanks
Mukesh