I've been admiring the brilliant Jupiter in the night sky for the last few months. So I was interested to read on Bad Astronomy that Jupiter would pass close to Mercury in mid-March before disappearing from our skies for a while. I've only (knowingly) seen Mercury once before, in a marvellous four-planet alignment in 2002. Phil Plait mentioned looking on 14 or 15 March, but those nights were cloudy. Last night was clear, however, so I looked out, just after 7pm. I saw a really bright planet, and then another, slightly fainter one down in the twilight, a couple of degrees below it. Aha, I thought, Jupiter, with faint Mercury close to the horizon -- no wonder it's so difficult to see!
But a quick check in the astronomy mags showed I had it backwards. The higher, brighter spot was tiny Mercury, and the lower, fainter one was Jupiter. Given how bright and easily visible Mercury was, I'm sure I've (albeit unknowingly) seen it many times before.
here's one from Greg Parker that shows almost exactly what I saw (except for the skyline details, of course).