For me, RSS is not really a useful tool for how I like to (or have to) use the Internet. My attention span is short enough that I don't spend lots of time on one topic - I get what I need and leave.
Having said that - it is definitely useful - especially those interested in new title alerts, monitoring a news event, looking for a job, waiting for new programming, or keeping up with a blog your really into. I do use RSS - but on an as needed basis.
I think in any web site design libraries have to consider promoting RSS as an option for keeping up on current library events and resources.
