I wanted the: "I will check out 4E first and will almost definitely upgrade" category.
I've upgraded 4 times before, I suspect I will do it again (DND to ADND to 2E to 3E to 3.5E). And I also suspect that unless it is really bad, a significant majority of DND players will get there eventually as well.
I also suspect that I will upgrade to 5E and 6E if I live that long.
My concern is that the time between upgrades has been fairly short recently (although one could combine 3E and 3.5 to 8 years from 3E to 4E since 3.5 really didn't change the mechanics that much): 4+ years, 10 years, 11 years, 3 years, and 5 years.