RSS was not completely foreign to me. I've been on LiveJournal for several years and have been getting the Unshelved feed there since 2006. I've noticed that the feed comes through before the email version.
For this exercise I set up accounts with both Bloglines and Google Reader and added feeds to both. The directions were easier to follow at Google Reader, but the "Sub with Bloglines" button that I could add to my Favorites makes it easier to add feeds there. There may have been something similar at Google Reader, but if so, I was unable to find it, and I had to copy and paste URLs. One feed (Pop Goes the Library) refused to add at GR but posed no problem at all at Bloglines. The "Manage Subscriptions" and "Settings" buttons at GR refused to work numerous times and I had to log out of the account and back in to change things. That got annoying very quickly. I like that GR will display feeds if you click on them again after marking them as read; there's at least one more step required at Bloglines. And Bloglines seems slower. "Help" is clunky at best on both sites. Logging in is easier at GR because you don't have to type in an entire email address. That in itself makes using GR more attractive to me.
I wasn't overly impressed with either Google Reader's or Bloglines' tools for finding feeds, but I just did random searches for subjects. Libdex was better, but many of the blogs listed aren't current.
How is this useful to me? For now, I'll use a reader to follow 23 Things on a Stick blogs. I'm enjoying reading them, and it's an easy way to keep up-to-date. The downside is that you miss looking at the actual blog pages themselves, and seeing the creativity there is part of the fun. I added some other library-related feeds, e.g. the YALSA and ALSC blogs, as well as some news and fun feeds. I'll probably end up deleting the latter two, because I just don't care enough about them.
I suppose feedreaders could be useful to our patrons, channeling information on certain subject areas to them. (Didn't we call this SDI way back when I was in library school?) This is certainly something we could tell them about. And I see that some libraries are producing feeds for their patrons (thanks, Linda!)
I don't think a feedreader is for me. Where news and entertainment are concerned, there are a few sites I like, and I choose to go to them on my terms. Feedreaders seem most useful for keeping up with blogs, and I'm just not that into blogs.