Twitter the upstart social networking site for people to write pithy 140 character statements and inform people what are you doing has been going through an upswing as of late. Oprah recently joined twitter and Ashton Kutcher holds the record for 1 million followers.

According to Nielson Research unique visitors to Twitter increased 1,382 percent year-over-year, from 475,000 unique visitors in February 2008 to 7 million in February 2009, making it the fastest growing site in the Member Communities category for the month. Zimbio and Facebook followed, growing 240 percent and 228 percent, respectively.

Twitter wants your attention, to improve its retention. A recent study conducted by Nielsen Company revealed 60% of users fail to return after a month.

I have to admit I joined Twitter and then stopped. I only came back because of the news and information I receive from the site from the likes of CNN, NYTimes and other tech tweets I also enjoy using Tweetie or my Mac and iPhone.

But–and it’s a big but–did Nielsen fail to take into account that many Twitter users start off using the web site interface, then quickly migrate to a third-party application? I rarely log on to the site, only to follow someone, and I would fall into that category. That’s the suggestion Brendan O’Connell offered up.

A quick look at Twitstat seems to back up his theory. Twitstat is tracking over 200 different Twitter applications and, as the chart below shows, only 27% of Twitter users are using the web interface:

Is this just marketing hype? Who knows, but if I know one thing for sure: statistics are really left to interpretation. I am going to tweet this right now.