One of the most useless feeds I have comes from a Chinese site, translated into English the title of the page the feed comes from is "Everyday English". Each time a new article is published it appears in my feed-readers with the title "Everyday English" and the text "Everyday English" that links through to the article. I have no way of knowing whether it is worth my while going to the article, each RSS item in my reader is identical.
At the other end of the spectrum would be the blog feeds where I can read the entire article in a feed-reader, inclusive of any included media files, the only reason to actually go to the site in question would be to read or leave comments.
In between there is a sliding scale, descriptive titles, snippets or abstracts included etc. etc. The bottom line seems to be I don't care how it works so long as I minimize time spent wasted going via links and finding I am not interested in what is at the other end. If I don't find my-self wasting time this way it is surprising how much information I can sift through and select from, every time I have to follow a duff lead though feels like a huge drag (probably way out of proportion to the time wasted but that is human nature). A feed that commits the double crime of not having a high enough density of compelling content and wasting too much time gets deleted.
Sometimes the outcome can be surprising, I had a number of feeds that produced very little of interest but sometimes the odd gem. Usually there was enough information in the title or link to spot something of interest. I decided that they were not worth close monitoring but occasionally I have time I might look to see what is floating on top there. A bunch of these types of feeds can be seen on my Netvibes potluck page.
Sometimes I use Google Reader on my phone via the Opera mini browser, it is very efficient so long as I don't waste time following links to destinations that have nothing of interest.
I guess content providers often want me on their sites but, what kind of mood do they want me to be in when I get there. The challenge would seem to be in giving me other compelling reasons to visit.
My final observation is that the usefulness of an RSS feed depends on the type of content and how I interact with/use it, I can only determine this over time and by having some interest in the content. So I suppose if you produce RSS it would be a good idea to get feed-back from people that meet these same criteria.