I really like the idea of River of News, dipping my toe in, and other related metaphors for consuming content on the Internet and letting it flow by.
The Drupal aggregator is sort of a river of news that Dave Winer envisions, except the aggregator isn't themable base on type of source. Feeds API is there, but I don't want items as nodes: content needs to expire and come back if it's truly important.
In my microstream I want to see:
Delicious bookmarks, using the API, not RSS
Twitter Lists, selected by checkbox but distinct (each individual tweet only shows up once) using the Twitter API, not RSS
Twitter timeline from multiple accounts (OAuth) using the Twitter API, not RSS
Twitter search feeds (multiple feeds) using the Search APl, not RSS
Identica, using the Twitter API-compatible Identica API
RSS feeds from blogs, I guess.
Notice a theme? It uses the various APIs of services, not RSS (or whatever syndication format), which is too limited.
This is probably work for Activity Stream, though it seems kind of limited in what (meta)data it pulls in.