Cog awareness
Reading some posts and other writings, including a recent blog entry by CDR, I gather that road racers are typically quite aware of exactly which gear they are in. I've had no need yet for such awareness: on most rides, even hard group rides, I float somewhere in the middle of my cassette, rarely hitting either the low end (which announces itself at the second-largest cog through cross-gearing noise) or the high end (only on descents). I guess I pick the gear that's comfortable, rather than deciding on a more analytical level which gear is the most appropriate for a particular effort. How important is it to develop a heightened awareness of gearing? Is it something you just pick up as you gain experience, or something to consciously work on?
By the way, what does it mean to be "on top of your gear"?