There's been a lot of hype over Bulldozer, but we really don't know much about the new architecture yet. Could be a flop, so I wouldn't get your hopes up. I'm sure it will be a nice upgrade over K10, but I'm not expecting a huge jump in performance. I think a lot of people are going to be disappointed because they're expecting a lot more from the architecture.
But anyway, I'd just buy based on your current needs and not worry too much about what's on the horizon. As mentioned Bulldozer isn't exactly close to being released, you'd still have quite a wait.
Also, what do you plan to do on your computer? Chances are you don't need six cores and a Phenom II X4 would be more than adequate for your needs. X6 won't help any with gaming, but it will provide a nice performance boost for highly threaded applications like rendering, encoding, etc. If you're doing a lot of work like that, though, you might consider Intel. More expensive, but they also offer higher performance.