The reasons why people use Twitter are probably as varied as the number of people on the service, some 7 million in total.

There’s a rather amusing video parody of Twitter posted by Current TV which pokes fun at people who use Twitter.

Whether you do have a good laugh at the video ( I did!) or see it only as confirming your suspicions that everyone on Twitter is a vacuous twit, one thing is clear – the growth in the numbers of people signing up on Twitter is non stop.

Market researcher Nielsen published new data on March 18 that shows dramatic growth in Twitter numbers over the past year in the United States. (To be sure you get that point with crystal clarity, CNET News says that Twitter’s growing really, really, really, really fast.)

Twitter.com continues to grow in popularity and importance in both the consumer and corporate worlds. No longer just a platform for friends to stay connected in real time, it has evolved into an important component of brand marketing. 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.

Nielsen has overall metrics that make interesting reading:

• Twitter site visits up 1,382 percent over the past 12 months
• The largest age group on Twitter was 35-49; with nearly 3 million unique visitors, comprising almost 42 percent of the site’s audience
• 62 percent of people visit Twitter.com while at work, while 35 percent accessed it from home only
• In January 2009, 735,000 unique visitors accessed the Twitter website through their mobile phones
• In Q4 2008, 812,000 unique users sent or received Twitter text messages from AT&T or Verizon cell phones. There was an average of nearly 240 tweets per person for the quarter

I found those last two metrics the most interesting as people can easily use Twitter anywhere they are from a mobile device, not tethered to a PC somewhere. Indeed, see what Nielsen says on that point:

[…] The ability to twitter via a mobile phone – whether through the mobile Web or via text messages – is a driving factor in the social network’s success.

That makes complete sense to me especially as there are many third-party Twitter applications for mobile devices that make it so simple to interact with Twitter and so your friends when you’re mobile.

The biggest scope for further usage growth, I reckon.

(Video parody hat tip Tom Murphy via Stuart Bruce)