Real D will distribute two National Geographic documentary films in 2007 giving them a wider theatrical release than they are used to. Real D is also working to bring their 3-D technology to more theatres nationwide. National Geographic has also decided to keep these films separate from the competition by making screening times during the day and not conflicting with show times for more mainstream films. These films will be geared toward a school-aged audience; they are expecting that most ticket sales will be to school groups for field trips.
I can't even remember the last time I watched a film in 3-D. It very well may have been the Honey I Shrunk the Kids show at Disneyland back in the 80s. I'm not even sure as to which theatres provide 3-D as an option in my area. I do think that National Geographic may be doing themselves a disfavor by not broadening their audiences beyond the young kids. As a fan of documentaries I think that it would be that much more of a draw to watch March of the Penguins in 3-D -- you'd actually feel like you were migrating with them, minus the possibility of freezing to death.