You know, it'd be great if the whole nation (GASP) voted on the same day. The whole election system is jacked up...electoral college? Come on.
Well, I'll agree with you that the electoral system is jacked up. But I disagree that the primaries should all be on the same day, and this is why.
In the past, there have been a few states with early primaries, and those have gotten all of the attention from candidates. We always hear about Iowa, New Hampshire, Florida, South Carolina, and California. A lot of the other states just don't get to see a candidate until campaigning starts for the general election, and in some solidly red or blue states, not at all; I didn't see a single major Democratic candidate in person the entire time I was in Georgia.
Now, folks are moving up. Primaries have moved up in Nevada and Alabama, among other states. Everybody's challenging N.H. to be "first in the nation." In the south, Super Tuesday was created deliberately to increase the influence of southern states, and what happened? With all of the primaries on the same day, candidates couldn't decide where to go, and they ended up just going to the ones with the most delegates. Instead of actual personal visits and attention to the voters, candidates have to rely on media and spin, which puts the richest candidates at the head of the pack at the expense of less-rich, but (potentially) just as qualified, candidates.
And suddenly you've got Giuliani running against Clinton, you've never seen either of them in person, and you don't know that there aren't two kick-ass candidates somewhere who never got a chance because they couldn't afford a Super Tuesday media blitz.
Now, I know it would take a little bit of math, but I'd love to see a system that wasn't so front-loaded that any candidate was able to cement a nomination early on. Keep California toward the end, for instance, and the candidates would be forced to spread out a little and pace themselves. Or, barring that, just assign primary dates randomly.