I don't use one for two very good reasons -
a) I don't have one.
b) The counter on my sink is too narrow to accommodate a conventional piece.
However, I am always on the lookout for one of those insulated or double walled contrivances that people use to keep sauces warm/dips cold at the table.
As I am a face latherer and would only use it to keep the brush warm between passes this would be an indulgence rather than a necessity, but should serendipity ever put one in my line of sight I should probably buy it.