For the fourth year in a row, the Center for Marketing Research at the University of Massachusetts Dartmouth has conducted an extensive study of how Fortune 500s use social media.

In 2011, Twitter use among the big names in business rose 2 percent over 2010 to 62 percent of all Fortune 500s. But just how effectively are they tweeting?

The study considered a Fortune 500 a Twitter user if they had an official corporate account with at least one tweet made over the past 30 days.

Using this framework, the researchers found that 308 out of the 500 companies examined were indeed active on Twitter.

This represents only a 2 percent increase over last year – a paltry increase compared to the 30 percent increase from 2009 to 2010.

However, Twitter’s slow growth doesn’t capture the fact that Twitter is the number-one social network of choice among the Fortune 500. 58 percent of the companies have a Facebook account and only 23 percent blog, compared to the 62 percent who Twitter.

All of the top 10 Fortune 500s have an active Twitter account, and nearly half of all Twitter accounts belong to the companies in the top 200. Those that rank higher in the Fortune 500 appear to be embracing Twitter more intensely than those that rank lower.

Google, ranked number 92, has the most followers of all the Fortune 500, with over 3,300,000. Next is Whole Foods, Starbucks and Southwest Airlines, all with over a million. Rounding out the top 5 is Washington Post with just under 600,000 followers.

Given the small, 2 percent increase in Twitter accounts this year, it’s possible that Twitter adoption among big business has plateaued. Perhaps the remaining companies are not “Twitter friendly” businesses, or are unwilling to give up some of the control they have traditionally had to their customers by connecting directly with them in a social environment.

Regardless, it is impressive that Twitter is the network of choice for the Fortune 500. Its open nature and simplicity are no doubt attractive features.

Do you follow any of the Fortune 500 on Twitter? If so, how are they doing? Let us know in the comments below.