From Wiki (Re: Snakes on a Plane): As of September 16, 2006, the movie has generated approximately $50,407,371 worldwide.
While I'm sure the box office receipts on this move aren't enough to justify the effort put into it (at least, as far as the studio is concerned), the marketing (Books, Wall Calanders, CDs, etc) along with the (very likely) millions they'll make from the DVD.. I'm willing to bet we'll see a second movie in this series.