A good idea for a Gregarius plugin, may exist already. The plugin gives a user definable list of keywords, if any are found in a feed then they are displayed highlighted within the article text.
Speed readers can have their favourite subjects leap out at them.
Compared with getting feeds of del.icio.us tags or whatever my scheme has the advantage that it acts like a rating/recommendation system rather than a strict filter.
However, I know nothing about the capabilites of Gregarius plugins.
Twitterings

This is easily possible. I added this to the wiki. Maybe someone will pick it up :)