The Solar Magnitude Forum concept is essentially that a given user will be most interested in topics that are either 1. very closely aligned with her interests or 2. unusually important and interesting.
The idea was initially defined within the context of the asynchronous discussion forum, but it could be extended further.
A couple days ago I came across this example from the Forrester site:
(larger screen capture)
Forrester is suggesting that I’d be interested in subscribing to newsletters that they assume as being directly applicable to my interests, and also newsletters that they assume I’d be interested in because they are the most widely read or broadly positioned.
The UI is simple and the app does the (relatively) heavy lifting of determining what the user would find the most interesting. The user is saved from paging through a painfully long list of all available newsletters to pick out the ones that are the most useful.