I’m certainly not the first to notice it, but many folks seem to agree that Twitter has recently hit an inflection point and is possibly (or maybe not) ready to begin monetizing it’s usage.

For someone like me who’s long social media in a lot of ways, I have to admit that I’ve been a later adopter of Twitter. But recently I’ve come around and have been starting to get it.

All of this has led me to wonder how best to measure the scope and impact of applications like Twitter, which are inherently multi-modal. Sure, I can both post and read tweets at Twitter.com but users employ SMS, IM, and various third-party client apps like Twitterific and Twhirl and others. You can see estimates of Twitter.com’s US traffic at Compete and Quantcast and of course worldwide at Alexa. Twitter’s own internal data showing 40% US and 60% OUS web traffic seems to sync w/ the Alexa info, but as you can see the three public traffic estimates diverge wildly.

Clearly though the web traffic only tells one piece of the story, which begs the question… how much Twitter usage is occuring on the non-web platforms? And more broadly, how can or should we as entrepreneurs and investors think about multi-modal consumer facing applications? With my product hat on, I’m thrilled that applications like this are being adopted by users across a variety of platforms in a largely seamless fashion. With my monetization hat on, I’m intrigued by the possibilities whether employing ad-based or freemium or other business models. My hunch is that Twitter will find some exciting ways to do so.

But I still struggle to figure out… how do we measure this stuff in a wholistic and effective way? I tend to think the whole is greater than the sume of the parts here. Apps like Twitter, in which users engage in a singular fashion across platforms, are fundamentally different than simply consuming a piece of content thru different channels. Go ask ESPN and they’ll tell you that usage of their website and their mobile/WAP sites are extremely different, whereas Twitter is essentially the same app no matter what means the consumer accesses it.