In only about 2 weeks time, the Decemberists have announced their new album, The King Is Dead, offered up a free single, “Down by the Water,” and debuted said single live on Conan O’Brien’s TBS show. Unfortunately, the song’s guest guitarist in the studio, one Peter Buck of R.E.M., didn’t make an appearance for their late-night performance tonight (okay, now I’m just getting greedy), but Gillian Welch showed up to provide her excellent — as always — vocals in support.