The web is abuzz about the iPad again and frankly, I’m stoked. There are a lot of things about the new Apple tablet that are interesting, from couch computing to a portable media player. But the feature I’m most excited about is Multiplayer.

Multiplayer what? Multiplayer games, multiplayer browsing, multiplayer video viewing, multiplayer productivity apps. Say that five times fast.

The iPhone is the powerful application platform, which enables developers to build awesome touch-enabled apps on the OS. The problem is the iPhone is way too small for more than one person to use at a time. A tablet computer the size of the iPad completely changes that, and enables full-fledged multiplayer experiences like you’ve never seen.

You’ll see people walking around with a portable electronic board game. Set the iPad down on a coffee table and start playing Chess. Take it in the plane and watch a movie with your girlfriend. Lay it down on your desk and draw on a two-person white board. The iPad will be the perfect size for these activities, and a whole new crop of applications will come about from the new screen size. The iPad will be like the Microsoft Surface, except portable and without the $10,000 price tag. This video of the Windows 7 touch interface might give you a good idea of what’s possible on the iPad.

Multiplayer on iPhone is already an amazing experience. Apps like Words with Friends and Tap Tap Revenge have shown both online (Words) and local (Tap Tap) multiplayer can work. But the iPad blows this out of the water by enabling a rich, local multiplayer experience on a canvas that developers can really leverage.

While at GDC, I met with many game developers who all pointed to this feature as the one they’re most excited about. It was amazing how many developers were already building iPad-specific experiences and it multiplayer was a common theme in that experience.

Multiplayer will also be a killer marketing feature for Apple. At a previous employer, I extensively studied how Apple managed to successfully market the iPod and one word summed up the whole thing: ubiquity. Apple managed to make it seem like the iPod was everywhere; that everyone had one and those that didn’t have one wanted one. The same thing was true with their marketing efforts on the iPhone.

Multiplayer on the iPad is going to quadruple that effect. You’ll see people at restaurants, at work, and even at house parties sit down and use the iPad collaboratively. It will be incredible to see all the use cases that developers find for iPad applications.