Demos have been something that Nintendo hasn't done well with. WiiWare and DSiWare has had the occasional demo for its games, but nothing that consistent, and demos disappeared after a while. The morning, Reggie Fils-Aime confirmed that the 3DS eShop will have plenty of demos for both retail and downloadable games.
I gotta say, welcome to 2005, Nintendo! Here's hoping the demos aren't taken down after a few months, so new 3DS converts can still try out some demos of old games.