Without question, the Internet phenomenon of 2009 is Twitter and Nielsen Online's usage numbers prove it.

Comparing unique visitors to Twitter's site in May of 2009 with May of last year shows a nearly 1,500 percent increase. Visits were up to 18.2 million, from 1.2 million a year ago. Time spent on Twitter also saw a dramatic increase, up 175 percent to 17 minutes and 21 seconds this May, from 6 minutes and 19 seconds last May.

Among those startling numbers, there's a dull one that shows time spent on the site by Twitter's users fell one percent in May, from April. Is this the beginning of the end for Twitter?

In my experience using Twitter and interviewing Twitter users at the 140 Character Conference in New York City last week, the end of Twitter is not near. In fact, its fame is likely to be around for years as more people begin using the micro-blogging site, pressured by those already using it. Only in the past month have friends on Facebook suggested that I and others begin following them on Twitter.

Speaking of Facebook, it has now been the number one social networking site for seven months in a row, through May, with 144.3 million unique visitors around the globe. It has been number one in the U.S. for five straight months, with 75.4 million unique visitors in May, up 190 percent from last year, according to Nielsen Online.

MySpace has made news with hundreds of layoffs this month, yet it is showing growth in video sharing. Nielsen Online reports that when counting total video streams, MySpace.com remained the top social networking site in May with 116.1 million video streams. Unique video viewers rose 23 percent from April, up to 12.2 million, from 9.9 million.

Anthony Massucci is a senior writer for DailyFinance. You may follow him on Twitter at hianthony.