I own both an xbox and a gamecube and in my opinion, xbox live is fun but can also be a PITA if you're a newbie to any of the games. Most of the gamers don't tolerate newbies, meaning more than likely you'll be kicked out of the game or in 1vs1 games like Capcom vs Snk 2, you simply just won't find any players. Like someone mentioned, you'll find a lot of jerks on xbox live, even more so than online PC gaming in my opinion.
I can understand Nintendo's take on online gaming this generation. At the time being, it's just not worth the investment. However, if their next console lacks online gaming, then, Nintendo is probably all done for.