They had, years ago, a clearly superior platform for event-driven programming (none of these weird callbacks). They have more or less failed to capitalize on it in terms of getting mainstream traction.

Here's some of what I think is wrong with Erlang:

http://journal.dedasys.com/2007/09/22/erlang

Several years ago, it was getting some "early hype noises", but sort of sputtered and bounced and never got off the runway.