Obama had a lot of independent and Republican support in the primaries, and there's no way to know at this point how many of those people would finally vote for him in he GE.
The polls do tend to show Democrats less united than Republicans.
I don't have a complete list of which states had open primaries or closed primaries, and who won each one.
I was googling this just now, though, and turned up a NY Sun op-ed piece from May 21
http://www.nysun.com/opinion/clintons-claim/76800/ near the end of the primary race, that said this:
In addition, closed primaries which only allow registered Democrats to vote have, except for Illinois, voted for Mrs. Clinton. Mr. Obama has tended to win states that allow independents and Republicans to vote for the Democratic nominee.
Again, I don't know if that's entirely accurate since I haven't found a list to compare it to and don't have time to look up all the primaries separately to see whether they were open or closed.
But Clinton did VERY well in states with closed primaries. And Obama's votes included people who weren't Democrats.
So there's no way to know at this point how many people who'd supported Obama in the primaries would be saying they wouldn't vote for the Democratic ticket if Clinton were the nominee instead. We had entirely too many people here at DU saying the same thing, Obama supporters who said they'd never vote for the ticket if Clinton were the nominee (and some saying they wouldn't vote for it even with Obama the nominee if Clinton were on the ticket -- talk about irrational spite), for me to believe that simply because those voters aren't willing to vote for Obama at this point, they were never Democrats. And for that matter, many Obama supporters here have argued that he could never have had Clinton on the ticket because even if she could help unite the party behind him, he'd cost her too many indepenent and Republican votes he might get otherwise. (The polls don't support that argument, but they made it anyway.)
I don't think it helps to suggest that most of those Clinton supporters now considering either staying home or voting for McCain weren't really Democrats. They were most likely centrist Democrats (I can't imagine progressives voting for McCain), but they're Democrats unhappy with our nominee, and I'm still wishing we had a unity ticket to get more of them back on board. Today's Rasmussen poll suggests Biden isn't helping with that.
So I'm crossing my fingers and hoping Obama can win their support between now and November. I don't want to see us lose this election. Especially since we should have been looking at a fairly certain victory with the party united. This was one year a unity ticket would have helped more than ever, though.