I'm a maybe/yes.
Maybe I'll buy it. I don't know what "it" is yet, so I can't say for sure. Timing matters; when 3E was on the horizon, I don't think my group had played 2E in over a year (maybe they had- college meant I was only there for summer and winter break, and when I was, we always seemed to be playing Shadowrun, a game I was also getting sick of). Skills&Powers gave a little more life to the game, but interest was waning. Learning of 3E was a godsend- something fresh, new, clean, exciting.
Now, I've got three active campaigns in various states, I'm planning my own "adventure path", and I've got ideas to reset my Game of Thrones and Iron Heroes games. I want to do something with Black Company, I want to run a War of the Lance-era Dragonlance game, maybe a 3E Dark Sun game, and I've got Rokugan and Arcana Evolved books just waiting for an idea. If Seattle blew up tomorrow and we'd never have anything more for D&D, I'm set for years to come. So, 4E needs to be something very good, an improvement over what I have now, preferably without disrupting things too much.
I'll almost certainly buy it at some point (unless it's crap, like, say, the wags who bring up collectible rules turn out to be right), but I'm not sure I'd buy it in 2008 or 2009. So, that's the the maybe part. But, if I buy it, I will almost certainly buy supplements, because that's the kind of guy I am. So, that's the yes.