I can see where signing up for a couple RSS feeds may be useful for someone with a couple of basic sites they visit each day. My husband has signed up for a science news aggregator that feeds right into his email each day, and he really likes it. However, to be honest, I know I’m unlikely to log in to one more site to check the feeds I requested.
As for libraries, an RSS feed for new items would be useful, if it could be customized by a particular subject or genre. I’ve known a lot of patrons in the past who love to see lists of newly acquired materials. Notifications of upcoming library events would also be a good use of RSS feeds.