Think about it...
If we were to go by the dictionary definition of social this article could be considered in itself irrelevant, so the aim here is not to disprove that by such definition Twitter itself is not a 'social network' but more that in the essence of what we mean when we refer to something as sociable is something that Twitter more often than not fails to achieve.
Whilst Twitter itself is not alone in this regard when it is compared to some of the older social networks its ability to facilitate something mirroring a genuine social environment is a short fall it can be highlighted on given its poster child association with the term social networking.
Twitter's competition. Who am I referring to here? Facebook, MySpace and even predecessors like Orkut (remember them?) and for those who like being tied into a service integrated with their GMail accounts, Google Buzz (to list just a few of the more common networks). These networks whilst not free of the Content Vs Noise ratio issues that all social networks undoubtedly contain do facilitate some things that Twitter does not.
Let's look at some of those things...
Ability to conduct conversations:
"Hang on! Twitter can surely do that!", you might say at such suggestions. This is true, it can, but not in any real or meaningful way. Let me explain.
a.) Any communication is typically limited to at most a few short / abrupt exchanges between parties involved. The ability to discuss any topic in any real way in even several 140 character tweets is something that the majority of people would fail to achieve.
This means that subjects of interest or topics that people have an interest in and people would engage with others in discussion over result in participants ending up finding themselves limited by the medium when attempting to conduct such conversations properly.
b.) Any more than a few exchanges between parties involved in a discussion is seen as poor Twitter etiquette. Even when / where these exchanges occur typically once discussions goes past several tweets back and forth their is usually an unspoken limit that is reached effectively terminating any further discussion.
The reasons for this can be varied including difficulty in discussing the subject in such short messages, the concept of wishing to avoid effectively 'spamming' other followers who also follow the persons tweets yet are not involved in that discussion and just general Twitter etiquette that discourages such practices (to once again ensure that people do not drive away their followers).
c.) The danger of miscommunication. When striving to ensure tweets meet that 140 character limit what tone/mannerisms and other aspects of communication are lost? In recent times on numerous occasions the writer witnessed and experienced situations where miscommunications occurred due to the nature of the medium rather than the intention of the tweeter where it was observed or agreed upon that due to the '140 character limit' the shared understanding of what was communicated had differed between the sender and the recipient.
Ability to present other forms of social commentary integrated within the environment:
As other networks do not have the 140 character limit it also means that it is easier to share topics for discussions within the confines of the social network environment itself. It provides a different user experience when a group thread or message thread can develop based around a piece that is posted.
Where the character limit is much more liberal things like news, opinion pieces, research and so forth can often be posted to such areas rather than users re-directed to links that provide no direct tie back to the original post and where replies are made via twitter it lacks any threading to see a discussions history / progress.
How many times have people encountered links to pages that contained little more than a paragraph or two of thoughts that would've served far greater benefit if delivered within the confines of the medium itself instead of re-directing users to an external website?
So what does Twitter offer?
A stream of monologues would seem the most apt description in a significant portion of cases. How many of the comments, opinions and so forth offered exist without the intention of seeking replies to what has been said? How much is self promotion, spam or idle commentary? Statistics seem to indicate a fairly large percentage is.
This is not to say that there are not brief exchanges that are facilitated by Twitter. But this makes this social network largely a rather unsociable place to be, after all how many of your real life conversations are restricted to a few lines of comments exchanged back and forth? Even communication between people via SMS tends to not be held back by some of the conventions and etiquette present on Twitter's service.
Twitter also offers the ability to share news, breaking or otherwise, links or anything else of interest and this is in the writers opinion its greatest strength. It does allow people to connect with others of similar interests and share knowledge and this too is a virtue, but at the end of the day this social networks greatest failure is its inability to facilitate a proper environment that people can truly be sociable within.