FWIW:
I like what I've heard so far with some of the changes for 4E. And, from what it sounds like, a fair amount of the stuff from 3.X ed. that isn't in the original 4E PHB may show up later in online articles or future products.
(Though, with that being said, [hyperbole]I'm not keen on having to wait for official gnome PC stats or a bard or barbarian class until PHB 18 is released[/hyperbole].)
I'm also not keen on losing gnomes and half-orcs for tieflings and dragonborn. I understand that their may be player demand for those races. However, I think in this case, as in the case with any of the "monstrous" races that were available for use as PCs, I'll place a limit on the number of said creatures in a party (usually only 1 PC out of the group may play one, or with really large groups, 1 of every 5-6 players, rounded down).
As it is, I know that I'll need to reboot & retcon my homebrew setting for 4E. The antagonism between paladins & warlocks (built mainly off of the AL restrictions of the 3.5 classes) will go out the window. Major NPCs will need a redesign or have to wait until future supplements because their races (PC stats) &/or classes haven't been updated yet (like changelings, gnomes, half-orcs, githzerai, warforged, barbarians, bards, monks, druids, sorcerers, soulknives, etc.). A major benefactor of the NPCs (and a beloved NPC of mine) will have to wait because the 4E MM won't have bronze dragon stats (apparently).
However, I can live with all of this. The retcon/reboot: I can deal with. I just look at it like it occurs in comics—a major event causes the reality shift to occur somehow (ala House of M or Infinite Crisis). The new PC races can be available, but rare & limited. The new/redefined classes won't be a problem. To be honest, the best way I think I can handle the changes in 4e is to preview them, establish limits that I feel are appropriate to the setting, and narrow the focus of what the campaign world is like (rather than having a lot defined at the outset). As more material comes along, I'll integrate it as I see fit. IMO, I think it's a bit easier to do this with a homebrew because it lacks the level of prior knowledge/expectation that players may have with established, detailed canon settings (like most/all of the existing D&D settings).
I'm cautiously optimistic about the new edition. To be honest, if Star Wars: Saga Edition provides any hints, then I'll be glad to not worry about allocating skill points each level (esp. for multiclass characters), worrying if a certain race is allowable due to monster hit dice or level adjustments, recalling the crit ranges & multipliers for various weapons, or worrying about my PC or NPC spellcasters' batteries running completely dry.
As it is, there isn't any canon D&D setting I prefer to use, because there's always some element to it that I just don't care for. And, to be honest, I find it easier to just use a homebrew setting instead of having to debate over "why it isn't like that in my FR/Greyhawk/Eberron/Dragonlance campaign" with players/fans that like/love/worship the status quo of the setting.
But, I'll have to wait & see before I make a final judgment (and Keep on the Shadowfell will be my first purchase, esp. for a decent preview of the mechanics). However, I think I'll make the switch as soon as it's affordable.