No one mentioned it in the thread so far. I am working in academia, and RSS is a lifesaver for us, to keep track of new academic papers. I am following around 50 journals, everyone of which publishes a few articles daily, at least. That makes around 1k papers/month. There's no way for us to check every journal website every morning. Twitter or Facebook are totally unsuitable for this.
My second constraint is that during my day, I use 2 different computers, a phone and an iPad to check on my RSS feed, depending on where I am and what I do. Reader was providing a flawless solution for the sync. There will be another one soon, that's ok. But according to my twitter stream, many, many people in academia are pissed off about this decision. I posted my feelings here http://wp.me/p1eIvd-d2