RSS -- or really simple syndication -- is how you are reading this post, unless you got it via e-mail, or surfed here directly. While it is closely associated with blogs, it's really useful for any content-rich environment that updates regularly.
Costolo really caught my attention with his take on media trends: that initially publishers tried to use the web to drive print subscriptions, and it didn't work well. Now they are trying to use RSS to drive traffic to their web sites, but that won't work either, because RSS is a new medium.
"The new medium never drives dollars to the old' it drives dollars to the new thing."
I think he's right. Which means that the importance of web content by itself will tend to diminish. People are not going to keep revisiting your web site to see what's there that might be new. They'll find out what's new when they choose to syndicate your feed, and you send them something new.
Of course, in this expanding world of communication overload, you need to have something pretty interesting to say if you want anyone to tune in. Authentic, transparent, and helpful. And maybe you can bundle some advertising messaging in there.