After writing a decent amount of Clojure recently, underscores do seem ugly, but I think I find commas even more annoying. I can accept underscores for the reasons raganwald mentioned, but having to write [1, 2, 3] instead of just [1 2 3] bothers me more than it probably should.
I noticed this too after using Coffeescript, going back to plain JS.
It's especially annoying when shuffling array elements or function parameter around: all items need to be separated by a colon, except for the last one, that must not have a trailing comma, making line swapping a nightmare. Drives me nuts.
