Find more information about them at Wikipedia http://en.wikipedia.org/wiki/Media_Bloggers_Association
You would not believe the power of the press to get free stuff and attend events for free. Now as a blogger you can get the same credentials as a reporter from CNN. For example at the Scooter Libby Trial bloggers got press credentials.
“After two years of negotiations with judicial officials across the country, the Media Bloggers Association, a nonpartisan group with about 1,000 members working to extend the powers of the press to bloggers, has won credentials to rotate among his members. The trial of I. Lewis "Scooter" Libby, the highest-ranking Bush administration official to face criminal charges, could "catalyze" the association's efforts to win respect and access for bloggers in federal and state courthouses, said Robert Cox, the association's president.”
The possibilities of going and getting free stuff as an official member of the press is staggering. For example the OMMA Expo in
“Members of the media are welcome and encouraged to attend OMMA Global Hollywood Conference and Expo, designed by and for the online marketing community.
To request credentials or for further information, contact Lou Rossi, email@example.com.”
In closing if you are a blogger think about the possibilities. The freedom of the press is written in the constitution. Bloggers unite and take advantage of this untapped opportunity!