With so may online services today, there's a need to control them in one place.
Current social aggregators such as friendfeed do that but you have to work for them first.
What do I mean by work? You have to manually add your username for each and every account you want to use! This is a daunting task that can take some serious amount of time.
But why do you have to this manually? There are many identity search engines today that do deep social search in the various data sources. Notably, spokeo.com which brings you astonishing amount of information given just an email field. So why the aggregators don't do that as well? Ask for the email field and discover the user's accounts automagically? Probably something that many devs are working on...
On the same topic, gnip.com aims to make the life of the aggregators much easier, by giving auto discovery services and API consolidation. Looks great - I'm going to check it out soon :)