I went up one tree hill with some friends this evening to try to see The Great Comet of 2007. Despite some cloud near the horizon, the comet was clearly visible once it got dark enough (about 9:45pm), with a spectacularly long tail arcing gently across part of the sky. It was certainly better than any of the other much-hyped comets that have appeared during my lifetime.
It's only supposed to be visible for the next week or so, so be in quick. It is apparently non-periodic, so if you miss it, don't count on catching it next time.