It's a potentially useful service that aggregates what your friends are doing around the Web into one big feed you can easily scan. In other words, if you've got friends who Twitter, friends who post photos on Flickr, friends who favorite videos on YouTube, and friends who tag music on Last.fm or sites on Delicious, this service will keep track of them all.
There are big issues with FriendFeed, though. The service only really works when your friends are also FriendFeed users. I do not like service that will not work unless the other friend is a user. I never have, I never will, so I am really disappointed in that. However, I do understand the reasoning behind it. Although you can add "imaginary friends" to non-subscriber feeds, but it is rather time-consuming and would rather the friend register.
There is a service similar to FriendFeed that is not too old itself, called Plaxo Pulse. I have used Plaxo for years and have always thought of them as great. They have really done a great job of keeping my address book up to date automatically and recently stepped into the social network atmosphere. I think if the trend continues, we will have just as many personal feed abrogators as social networks and there will be aggregators to aggregate personal aggregators. Silly, huh? It will probably happen.
So I really enjoy FriendFeed. It is simple, fun, and makes my online life a little easier. One things I would like to suggest is an auto-finder. I join, and FriendFeed finds all the networks I am involved in using my email address. Otherwise I have to add them all myself, and my friend Matt that I track, has to add all his networks also. Not a big problem, but I am sure can easily be fixed.
Try it out. It is now available to the public and it is FREE - One thing that everyone loves.