Ayende recently posted his feelings about how Twitter can be misused from time to time.
You cannot have a meaningful discussion in Twitter or IM, the conventions and limitations of the platform. Email is a better medium to expression complex concepts, but voice or video are far better methods of communication.
I'm inclined to agree, though some people will indeed be able to have discussion with some meaning, its hard to have a discussion about a complicated set of ideas.
I'm fine with a discussion between two people going forever and a day on Twitter. I'm not having a go at anybody who does. As Chuck says: let the tweets flow. It's just that the discussion is bound to be fairly light and easy.
I do think there are a few circumstances where Twitter's weaknesses as a communication medium/archive are exposed.
Firstly, if things are busy in your twitterhood, spanning tweets may have the opposite effect that your looking for; if other people tweet in between your tweets, it will dilute your message.
Secondly when you need to use around 5+ consecutive tweets to get your point across, it becomes clear that you simply need more characters per message. Spanning across multiple tweets to get an idea across is fighting against the tool.
Should Twitter increase the char count? I feel the higher the char count goes, the less Twitter looks like a microblog engine and the more it looks like usenet anarchy. I happen to like SMS updates too so I feel it would break out of the SMS boundary.
Lastly, for conversations that occurred while I wasn't obsessively staring at Witty, its kludgy to find the beginning of the discussion and then skip other peoples tweets that occurred in between. To be fair, that's not the fault of Twitter, and hashtags certainly make it easier to listen in to particular topics (much like IRC Channels) but most clients behave the same way.
These few problems alone make Twitter a deal breaker *for me* when it comes to heady topics. Emails, blogs, and wiki's are ways in which I like to escalate such things. But if you like to contemplate quantum computing in 140 char chunks, more power to you.
Incidentally, this was around 2200 characters or if you prefer, 16 consecutive tweets.