For you guys who are saying it's a "HORRIBLE" format -- well, live with it, because that's the STANDARD format and it's pretty much expected by ANY respectable production company that your play will be formatted like that.
It's not like it's just a "suggested" format by some random company. That's THE format. EVERYONE who knows what they're doing uses that format. EVERY piece of playwrighting software (e.g. Final Draft, which is also THE software used), handbook, guide, etc. will follow that format. It's the format that's been developed over quite a few hundred of years.
But you say -- oh, what about all these books and such of plays that don't use that format? The books are formatted like that because they're BOOKS. Are books published in the manuscript format that authors submit to publishers? No. But you sure as hell wouldn't format a manuscript in landscape double-column and submit it to a publisher.
If you really want more reasons, go back to the site and read their little thing.
[note: I just realized that I came off a little absolute. Let me clarify: you don't have to follow the EXACT format that THAT link provides -- the example pages on THAT page are not the universal standard for everywhere. BUT, you DO have to follow the "rules" that are followed by that format -- the most BASIC of which in playwrighting is the APPROXIMATE CENTERING OF CHARACTER NAMES and DIALOG RUNNING ACROSS THE PAGE. ]
[edit two: Here's MORE information.
http://www.playwriting101.com/chapter05
http://www.playwriting101.com/chapter06
On dialogue:
http://www.playwriting101.com/chapter11
http://www.playwriting101.com/chapter12