Since the beginning of the year, I’ve noticed more and more mainstream media mentions of Twitter.  I’m sure some of this momentum is attributable to the much-publicized usage of Twitter by the Obama campaign – the now-famous “We just made history” tweet. But last week’s Sydney Morning Herald ran an article about Daisy Turnbull (the daughter of the Australian Federal opposition leader) and who she “allowed” to follow her on Twitter (like locking your account was somehow bad), and by then I knew that journalists had descended into “let’s write a story each day using the word Twitter” frenzy.  And this weekend’s Herald Good Weekend magazine carries an article about the Twitter founders themselves.

We talked a little about this in the office - we’d been using Twitter internally, and I’d just decided to open up my own tweets to the world as a sort of “public” face to Locatrix.  (We might yet add another Twitter account to better serve this purpose). Others were noticing that Twitter had somehow jumped the chasm into mainstream.

You could argue that Facebook, at 175 million and counting, had made this leap ages ago.  In fact, recent articles – including Fortune’s cover story on Mark Zuckerburg – suggested that Facebook has well and truly moved beyond the tech-savvy and Generation Y.  I have several of Uncles in my Facebook list, so I can attest to this fact.

This week, however, we’ve seen two interesting stories emerge.  One was apparent in light of media coverage of SXSW and the purported “domination” of that event by Twitter. Seems half the planet (or at least those attending the event in Texas) were attaching “#sxsw” to their Tweets to the point of saturation; there were suggestions of service and information overload, especially for those trying to access Twitter on their mobiles. (Oh, and the 1,382 percent growth of Twitter ). The second was a moderate (but quite valid) public backlash over Facebook’s new look. I’m not suggesting that much gloom for the Zuckerburg set, but it will be interesting to see if and how much their time-on-site metrics trend downwards in coming months.  (I’m know I’m using the new look site a lot less than I used the “old Facebook”).

Which leads me to the question in the title: Is Twitter the new Facebook?

My thesis is this: the simplest interaction with Facebook is the one-line status.  Mark is happy.  Mark is sad.  Mark is in London today.  Mark is working on a Series A funding round. All things I post to Facebook, all things I read about my friends (or those that care to post) which keeps me – to use the Zuckerburg vernacular – “connected”. For a lot of people, this is their only input into Facebook.

Twitter, on the other hand, is just this, only searchable – a nice feature.   No weird site redesigns, no getting used to applications only to have them disappear, no over the top legal agreements – and no constantly-changing restrictions on what you can and cannot do via the API – I know folks who never touch the Twitter site itself, updating and managing accounts via one of the many publicly available third-party tools, like Twhirl and Twitterberry (my tools of choice). So not only is the barrier to participation lowered to a bare minimum, its relatively open.

What remains to be seen is just how will Twitter (or any number of social networking services) create a sustainable business model. Their latest funding round leaves them cashed up going into a user upswing; from here its all about creating a model which doesn’t alienate existing users/fans, and old-fashioned execution.

Neither of which seems a strong point of the Facebook crew.