Yes, the battens, which are flexible, provide curvature to the entire sail when filled with wind, allowing for better performance.
I'm not sure what you mean by "special attachment to the mast." Unless the main is a gaff rig, the sail has cars attached to the luff which are inserted in a slot on the aft side of the mast. The cars "slide" up the slot when the sail is raised. This is the standard protocol for the typical fully-battened mainsail.
Most cruising sailboats these days have a mainsail that is pulled out of and rolled back into the mast. This type of sail cannot have any battens.
There is a more recent technological advance that allows a sail to have full battens and also be furled completely. This is the boom furler, a boom that is much larger than the standard boom, to allow the sail to be rolled down into it, battens and all.
The principal advantage of a fully-battened main is better shape and thus better performance. The principal advantage of an in-mast furling main is that it has "infinite" reef points. The boom-furling main would seem to cover both of these items.
Last edited by SailinJay; 02-08-2007 at 05:44 PM.