Robert Scoble, recently made the following comment, assuming that people use Pownce versus Twitter…
All you “pro-Powncers” are assuming one thing: that Twitter isn’t going to come back. I’ve heard rumors of a soon to come update. I love competition!
Am I crazy or do Twitter and Pownce fill two completely different needs?
Twitter is here to answer the question, “What are you doing right now?” It’s for quick short status updates. It’s the Web 2.0 version of IM away messages.
Pownce is to send stuff (messages, links, files, and events) to my friends. It recognizes that we all too often just want to send something quickly to someone. It doesn’t feel like it should deserve its own email. Plus things too often will get lost amongst the clutter of email. Pownce is just like writing on someone’s Facebook Wall.
What would be great is if one of the options in Pownce was to send and receive Twitter updates.
Twitter updates are just one more type of content that you send to your friends.
Oatmeal Stout - Justin Thorp's blog 
I already have enough social networking tools? Why not just write a facebook extension?
I want life to exist outside of Facebook.
Facebook is turning into AOL (circa 1990s).
I just re-read your comment and realized you weren’t talking about what I’m about to argue about it, but I already though it out so I’m going to say it anyways.
How are Pounce and Twitter going to not turn into AOL? You are an early adopter of technology. Most early adopters are not “AOLesque”, but as the mainstream market catches on to what the early adopters already use, the character of the social network changes. What used to be cool and elite is suddenly filled with average Joes, a la myspace or AOL.
(Now, on to what you were really saying…)
I keep noticing that you keep talking about this or that social networking tool, and you keep jumping from one to the next. But most users don’t want to have to use a million different sites/tools for what they do, they tend to find one site and stick with it. That’s why facebook is nice, because of the large population of the world using it, and the fact that it’s not able to be customized as much as the crappy, ugly myspace.
Pownce and Twitter are very much different.
But I find that some of those using Twitter are forever comparing the two and somehow manage to come to the conclusion that Twitter (being little more than the unloved half-cousin of the Status update on Facebook, but with a smaller character allowance) is “better” than Pownce.
Rather than use Pownce for threaded chats, they bend Twitter all out shape and spread their dialogue across multiple tweets, which is just insane.
So now I just don’t like Twitter…