At my shul, during Musaf of Rosh Hashanah (and i think Yom Kippur as well), they sing the piyut ויאתיו כל to the Carlebach tune. At the end, a large percentage of the community gets up and starts dancing around the shul.
On a day when we don't even say hallel, is this appropriate behavior? (Perhaps it depends on your philosophy, Chasidish or Litvak.)