I believe the stance the Long Now Foundation takes is; this current evolution of human has been around for roughly 10,000 years based on the fossil and archaeological record, yet we think and plan in ever smaller futures. Their idea is that if we've been around for 10,000 years, assume that we could be around for another 10,000. Generally, we should consider a longer future than the next weekend, fiscal quarter, news or election cycle. Also, if we started to think (and act) in longer terms our decisions would be very different.
As an historian by profession, I have to side with Chris. 10.000 years is absolutely nothing at all if you consider the history of our planet as a whole. I don't even understand why they talk about 10.000 years (aside from being a round number). The human race has existed for a lot longer than that.
The idea that we should think long term instead of just a few years or decades ahead is by all means a positive one. Had the humankind actually considered the impact our actions are going to have in the many years to come, the future of our children and great-great-grandchildren might look less bleak.
Still, the idea that we can somehow prepare for the next 10.000 years is, for lack of a better word, useless. We would need to be able to predict future if we were supposed to plan for it. History is a great teacher but it cannot foretell the future.
People always make preparations based on their past experience and that's why we're never properly prepared for whatever disaster does happen eventually. At the outbreak of WWII most military thinkers were expecting trench warfare on steroids but what in fact happened was something totally different (different even from what the most radical military theorists predicted). The US arrived in Vietnam equipped to fight hordes of Soviet tanks on central European plains but the real enemy were guerillas hiding in the jungle. Everyone was already well aware of terrorism before 9/11 but the thought of anybody flying a couple of passenger jets into WTC would've been widely dismissed as science fiction just days before the attack. Goes to show we have no idea what's going to happen in the next few months or years, let alone a few millenia.