Now and the Future:
It's fun to see the evolution of handheld multiplayer. These days handheld rely on wireless connections instead of link cables. Not to mention, players don't need to be in the same room anymore to play multiplayer. Some may argue online handheld multiplayer is diminishing the experience. However, unlike console and local multiplayer, handhelds aren't abandoning the old style of local play.
With the release of the 3DS and PSVita this year and knowing how these handhelds will connect to their respective home console, handheld multiplayer will get better and better. Especially if handheld/console connectivity catches on in the future, gamers may see more varied, unique multiplayer experiences with their handheld. Hell, multiplayer may be what will save handhelds from dying off.