I game with a bunch of guys in their 30s and 40s. Some, like me, played 2e, but a few of them played 1e as well (and they've still got their books to prove it). All of us are relatively inexperienced with the 3.5 ruleset and none of us are particularly enamored of it. There are a number of problems we have with it, but the only one I'll mention here is the one I have the biggest issue with: the amount of math required to adequately prepare for a session. I'd much rather be spending my prep time as DM doing creative stuff and using my imagination to come up with interesting plot hooks, memorable NPC personalities, and so on. Instead, I spend the vast majority of my time doing math - both in developing NPCs and monsters and the like and in "double-checking" the PCs' stats to make sure the math is all correct there too. I don't find it fun at all but I'm much happier as a DM than as a player, so I put up with it.
4e feels like it's been designed with me in mind. The designers appear to be addressing every single issue I have with 3.5, and they're fixing those issues in ways that make me happy. 4e definitely has "this is for you" written all over it.
What I find amusing is that it seems like most of the 4e-haters are older gamers (forgive me if I'm wrong, but that's the impression I get) ... yet my group is composed entirely of older gamers who are virtually chomping at the bit to start playing 4e.
So yeah, I'm definitely in the "already switching" camp. I've preordered the now-discounted core book gift set as well as H1 and H2 (there's no need to jump the gun and preorder absolutely everything, but I'll probably get the FRCG [more to plunder for ideas and mechanics than for anything else], H3, P1, DM Screen, Tome of Treasures, and Martial Power ...)