Obligatory (somewhat belated) Columbia post
First of all, my condolences to the astronauts' families, and really everyone in the space program. Their sacrifice will not be forgotten.
But that's not really what I wanted to talk about, since many people have trod that ground already. My concern is really: where does the space program go from here? The Shuttle is (was?) an incredible feat, reducing the feat of going out into space from inconceivable into something we thought of as nearly routine (with this a rather rude reminder that it wasn't, after all). But I felt that after Challenger, NASA became a little more timid in its approach. Rather than continuing to push the frontier into new and exciting missions, they contented themselves with staying what they already had and were comfortable with. Not to say that there wasn't an awful lot of valuable science done on the Shuttle missions (John Glenn aside) -- but it really represented to me a failure of the will to explore new frontiers, and this disappointment only got more acute as I saw the new and truly innovative programs (X-33, for example) die for lack of political will over the Shuttle. Gregg Easterbrook presents a much more forceful case that the Shuttle should have been scrapped long ago; I can't say I completely agree with it, but the fact that the Shuttle has pretty much precluded NASA from undertaking other large projects is quite unarguable.
My hope is that this will finally kick NASA into expanding into things we should have done years ago. My fear is that NASA will become increasingly timid and we'll become even more reluctant to expand the limits of human knowledge.