Socialthing!
I have been trying out the latest Buzz on the net called Socialthig! (socialthing.com). It's still in beta but looks very good and they are working very hard to make it even more great.
In Socialthing! one can post and view a bunch of other social networks, at the moment:
Posting for twitter and pownce are available, more to come i am sure.
This is the first service i try of this kind and find that having everything aggregated in one spot just saves a lot of time, keeps in track of friends from other networks and allows one to manage much more services in a more comfortable manner.
Socialthing doesn't get in your way, it offers a "Just Works" way of getting everything you need from the sites they enable. I miss ma.gnolia support by the way, but i am certain they will enable it soon enough.
I am sure they are working hard to make everything available to everyone in a stable manner, you can even vote for you favorite service to get support.
Anyway, don't take my word for it, if you can get an invite, take a look @ it :) i have two to give away, just drop me a line if you are interested.