Twitter. I’ve been using it very little since I created my account, mostly due to the fact that I could not find a suitable desktop (or laptop) client for Mac OS X.
But now I have found one, it’s called Nambu and it has all those nifty features you want and it runs natively in Mac OS X. You can search the Twitter network and most important of all, you can use it to update and follow all things associated with multiple accounts.
I currently have about six or seven accounts in Nambu, two for Brutal Penetration, one is my own and one is for Neverhood Clothing, a little clothing brand a friend and me have been running for a few years now.
Hope you’ll try it out, it’s being actively updated by it’s creators who are very helpful (on Twitter, offcourse).