Here's the link to the press release for this new feature:

http://finance.yahoo.com/news/southw...150000487.html

$40 at the gate gets you to at or near the front of the line. Doesn't look like any other sorts of upgrade perks (like more FF credit)...just a boost to the front.

It says that a limited number of these upgrades will be sold, though I'm not sure how many. *If* these are essentially early boarding slots to allow you to grab the added leg room of exit row, I'm still not sure it's really worth it. On a thru flight some or all exits may be taken. And if you're going for exit, it can matter a great deal if you're A2 or A8 or A14, especially if you hate middle or are flying with someone you want to sit next to.

EDIT: Apologies for posting the link already posted -- I had my posting incomplete on my desk when I got side tracked. By the time I finished it later and posted, someone else had already posted the link.