It is interesting that the post that I get the biggest response to has to do with a kid who doesn't know the difference between marvel and DC.
It would be an interesting story, but I think the days of a DC/Marvel cross over are pretty much over.
Now don't get me wrong, I used to read both Marvel and DC along time ago.
I am the first to say the the Best X-Men was when Claremont and Cockrum did it, but Marvel got too confusing to me and I stopped buying the titles.
DC and I have almost a 50 year relationship. I went with what I know and have rewarded with great stories.
So.... until DC and Marvel do cross overs like "JLA VS Avengers", I will always reject Spider-Man for membership in the JLA.
Go Forth and Do Well.