The best thing, for me, about Google Reader is that I can use it from work or home without worrying about synching things back and forth. It knows what I've read, and what I haven't, and I don't need to keep track of anything myself.
Open source and works wonderfully well. Also, easy to mod. I put in a Pinboard.in sharing link for all my articles, and you can do the same with just about any service in a few minutes with PHP.
