I'm slightly concerned about the requirement of minis, as our group has never really used them on a grid, mostly just setting them out to get a general idea of where everyone is, and that's only been a recent(within the last couple years) development as we ran into way too many instances of misunderstanding where someone was.
We just started(last week) trying to use an actual grid, and it didn't work that well, but part of it I attribute to the inane setup one of the guys did(our group in one corner, the bad guys in the other, so everything was an angle), and one of our players has confided in me he despises the use of the grid, and that he hates the diagonal movement stuff, when I told him 4e was switching to 1-1-1-1 movement, he said that was even worse.
I'm not sure if we're giving it another shot tomorrow night. I'd like to, but it's a democracy.
I think part of the bad experience was that we had never used them in that way before, and counting squares seemed like a needless thing when we were doing fine before. From the characters and rules we've seen so far it seems like 4e will hinge slightly more on the use of minis, but I don't think it will be impossible to play without them, and we'll likely continue with the minis but without the grid. The only issue I really forsee is the use of shifts outside a grid, but I don't think it should be too hard to figure out.
I hope anyway. I honestly don't mind a grid system that much, so if it's required for more streamlined play, no big deal to me...it's the other players in the group that will be adverse to it.