Copy is directly from them...I'm including here as a reference...there's a habit of not being able to find the information again once you accept a change from FB. So planning ahead, here's what to look for.
By choosing to upgrade your page, visitors to your page will begin to see the new layout, and you will not be able to revert back to the previous layout. All pages on Facebook will appear in the new layout beginning March 2011.
We encourage you to alert any other admins of your page before upgrading. After upgrading, Facebook will send your other page admins an email alerting them of this change:
"Are you sure you want to upgrade Marketing, Advertising, Public Relations from Always Visible Signs right now?" (Obviously, your page name appears!)
The new feature for which I'm most grateful is the "New Settings" which will allow me to post to my Page versus my Profile as a default. This is HUGE and a tremendous time saver. Thanks, Facebook!
Please note their comment: All pages on Facebook will appear in the new layout beginning March 2011.