"What are you doing?" is the question. The answer is most likely "Not much."

But for twitterers, that's almost beside the point. 

The point is to keep fellow twitterers thoroughly informed on exactly what one is doing at any moment. This is done via SMS messages from one's phone in no more than 140 characters. The twitterings are then posted for all other twitterers to devour.

Twittering may sound wacky, and perhaps it would be to many people, but it's the latest twist among many new twists in the fast-changing world of social networking.

While MySpace is by far the dominant social networking site, Twitter.com, while ranking only 1,739 among U.S. internet communities and chat sites, represents the increasingly niche nature of social networking.

“Some of the fastest growth is coming from smaller sites, even though they are still really small compared to MySpace,” says LeeAnn Prescott, director of research at Hitwise, the web tracking firm.

And that's as social networking overall continues to see mushrooming growth. In just one month, between January and February, the market share of visits to the top 20 social networking sites grew by 11.5 percent, to account for 6.5 percent of all internet visits, and that comes atop a growth pace of 87 percent from February 2006 compared to this February. Says Prescott: "I don't think that it is a category that will stop growing in the near future."

MySpace still holds an 80.7 percent market share among the top 20, as of February, with No. 2  Facebook at 10.3 percent. MySpace outperformed the overall growth for the entire category, with visits to the site this February up 107 percent over February 2006.

"It is still taking off," says Prescott of MySpace. "More people are catching onto social networking, and I would say they are visiting it more often. For a lot of users, visiting MySpace is part of their day, and they are visiting it several times a day."

But interestingly, MySpace appears to be driving a good share of the traffic to some of the smaller, faster-growing sites, passing down visitors as a bird might pass down food to its chicks. In fact, Hitwise found that one in every four visitors to the smaller sites is actually coming from MySpace, up from one in five last year.

“MySpace is the leading source of traffic for these sites, so that means that people are maintaining profiles on MySpace and other (sites),” says Prescott. It's a case of people wanting to keep up with different groups of friends, and also different interests.

Particular momentum is building up around communities aimed at music and other media. Buzznet, a video and photo-based community, saw its market share of visits grow 148.4 percent from January to February, while iMeem, a music community, grew 145.7 percent. At MySpace the comparative figure was 10.2 percent and for Facebook, 9.1 percent.

Meanwhile, in online ratings for the week ended March 4, the top five parent companies were Microsoft, Google, Yahoo, Time Warner and News Corp. Online for the sixth straight week. The top five brands were Google, Yahoo, MSN/Windows Live, Microsoft and AOL Media Network.

Experian Group Limited was the top advertiser with 11.23 million impressions generated, followed by No. 2 NexTag at 8.07 million, both well up over last week. With 28.81 million ads served, Yahoo was again the top advertising site, more than quadrupling No. 2 MySpace at 7.11 million.

Sessions per person per week were down one from last week to 16, with domains visited per person also slightly down to 39. Average PC time per person per week was down nearly 4 percent to 16 hours and 48 minutes.