I'm with Gallus Moll, Auldtimer, EKanne and Diva on pretty well all they've said. And I'm not with ER or Keltickev (mainly - definitely do NOT change the tune to Slave's lament - or even funk up the usual tune, as some have done it is a LAMENT!)
And one thing that really sticks in my craw is that in our ceilidh band we have to do a set of "Burns Waltzes" and "A Man's a Man" has been turned into a waltz! Heaven preserve us!
I am trying to learn "The Gloomy Night is Gath'ring Fast" - another very miserable one, to the tune of Roslin Castle, which is somewhat of a challenge in range and pitching.