For normal people there's already a tool that does that: Facebook.com. Facebook is the Internet for a huge % of Internet users. I don't even think there is a pain-point.
There certainly are a few (at least) pain points with Facebook, even for "normal" users. Spam, for one. Something that makes it a little more accessible could take off, but a competing browser may not solve the pain points.
In all seriousness, what would that tool do? There may be a market for an app that will allow you to consume/manage your Facebook, Twitter, Tumblr, etc, from one central location.
OK. In all seriousness, my personal preference is a tool that would a)let me tag every connection, feed, and post arbitrarily, b)display the most common connections/posts/tags/posts-from-connection-tagged-x easily, c) let me specify tag groupings via drag-and-drop and command-line regex, d) handle all logins without jacking my privacy.
I'll pay you zero dollars for it, but I'll let you show me relevant ads on alternate Thursday. You in?
I just don't see this as a viable business (big enough market or a market sustainable by charging a large enough margin). It'd probably be a fun project to take on at one of the Hack-Weekend type events.