Flickr photo via Limbo Poet.

I am not calling this a bubble -- at least not yet. But in the past 24 hours, I've received product pitches from three Seattle area entrepreneurs touting new Twitter applications.

Yesterday, it was Marcelo Calbucci's new service TweepML, which allows users of Twitter to easily follow large groups of people with one simple click. Since then, I've come across TweetsLounge -- a Peter Boctor project which is being touted as a Yelp-style directory of Seattle area businesses on Twitter -- and Tweetiator -- a patent-pending offering from Seattle's NimbleSource that provides Twitter users with link sharing stats.

That follows last week's story on CrowdEye, the Twitter search startup led by former Microsoft executive Ken Moss.

Entrepreneurs are salivating at the opportunity to build something cool and useful around Twitter. But is that really smart?

It is entirely unclear whether real businesses can sustain themselves on the Twitter platform. And many of the new projects now forming aren't quite focusing on the revenue potential, instead trying to make a dash in the great Twitter land grab.

"We believe that continued growth in Twitter usage will drive further value not only into Twitter, but into the entire ecosystem Twitter is creating -- including apps like CrowdEye," Moss recently told TechFlash.

Maybe. Maybe not.

We've chatted in the past about the difficulties in tying your fortunes to another's platform -- whether it is the iPhone, Facebook, MySpace, Microsoft or Twitter.

We've already seen some carnage in this arena, most recently the very soft valuation given to Seattle online music startup iLike which rose to prominence on the back of Facebook only to sell out for a reported low ball price of $20 million.

But there are other examples too. Madrona Venture Group and others decided to pull the plug on Bevy, an online shopping application built on Facebook. May developers also are finding it incredibly difficult for their iPhone apps to rise above the clutter.

In fact, the entrepreneurial challenges of building applications for the iPhone was the subject of a panel discussion I participated in a few months ago on KUOW 94.9.

"... The developer in this ecosystem is really taking on a lot of risk and it is not an environment which you can count on sustainable revenue," iPhone app developer and Voicebox Technologies exec Victor Melfi said at the time.

So, where does that leave us?

Certainly, Twitter is a new communications phenomenon -- as evidenced by this recent discussion on TechFlash about the microblogging service being taught in the classroom.

But as a business opportunity?

The jury is still out on that.

[Flickr photo via Limbo Poet]