I currently use Google Reader to subscribe to and read RSS and Atom feeds. It has pros and cons.
One of the great things about Google Reader is that its entirely in the cloud. I can access it wherever I am, whichever operating system I'm using. Also as its run on Google's servers, they pay the bandwidth bill not me. I subscribe to lots of feeds (181 as of now) but I don't read them all all the time. If I don't want to read some high volume feeds I don't open them and they don't get downloaded to my machine. This also means that its Google that checks the feed for updates all the time, not my machine. And that's the beauty of using a cloud based feed reader. Google only has to download the feed 1 time for all the subscribers of that feed in Reader, not once for each user.
This is the sole reason I use a cloud based reader, and this pro is too great to get me to switch. Unfortunately there are some things that I don't like about reader and some things I wish I could add. That's the bad thing about using a cloud service like this, I cannot edit the code for my needs. Open source desktop applications can, but with Google's cloud services you cannot.
Its good that in Reader you can download a list of your subscribed feeds, but I wish I could also download the feed items themselves in bulk. There is a copyright issue here that being, from what I've experienced when you subscribe to a new feed in Reader you can view the past postings going back probably to when it was first indexed, despite these items no longer being in the feed. I want to be able to download those too. I guess since you are already downloading them when you view them this is the same, so its not a new issue.
This is turning into a debate about cloud services vs. desktop software, so I'll stop here.