Or actually, this post is a response to Robert Scoble's (http://twitter.com/scobleizer) list of five reasons Twitter *isn't* for conversation - when I really do think conversations of a key aspect of what makes Twitter social. However, I agree that people abuse conversation on Twitter, but that's just because they don't know how to do it well.
The way to have a conversation is to make sure that every reply you post is recontextualized. Put in the proper subject nouns, avoid pronouns, and make sure that you re-reference the topic of conversation with each post. That way, others who see your post aren't lost and can jump in and take the conversation in new productive directions.
Now, specifically to respond to Scoble's complaints:
1. If you get into something with one other person all your other followers will start complaining.
Not if you apply the rule above. Your replies will seem like brilliant original thoughts. They'll have a way to jump in instead of being mystified.
2. You can't "thread" and "capture" a conversation.
No, you can't, at least not in Twitter itself. But why do you want to capture a conversation on Twitter anyway? Twitter is ephemeral, and I already have too many stored bits of data in email and elsewhere. I actually like that the conversations go away after a time, making new mental space for more thoughts.
3. Most people on Twitter that are joining lately are not people who participate.
Well, I haven't found that to be true. And even if it were, why should that negate the potential of having your own conversations? Maybe people aren't participating with Scoble because Scoble isn't replying?
4.Twitter's expected usage is "what are you doing?" Not "what would you like to chat with your friends?"
Even Evan Williams (twitter.com/ev), CEO of Twitter, says that the "what are you doing" headline is no longer appropriate for the posts on Twitter. In fact, I find the "what are you doing" posts the most boring: chats and resources the most interesting.
5. You can't bundle up a conversation and save it for later.
Maybe true. And I agree that Friendfeed and blogs offer a great way to archive conversations. If you want to do that. But Twitter is about the Twitterstream, dipping in and dipping out. It's valuable precisely because, like IM, it ISN'T archived. And as far as being able to archive some conversational threads, or follow those threads, this may be an enhancement of Twitter that will surely eventually come. It doesn't mean we should stop having conversations now.