Paul Vick nails it:
[W]riting a new language, domain-specific or not, is a lot like opening a restaurant: everyone thinks they can do it because they’ve eaten at one and it looks like fun.
via DSLs: Definitely a bad idea! .
He's getting some heat in the comments for his intentionally-provocative title, but I think he's exactly right -- most languages, whether domain-specific or not, turn out to be more trouble than they're worth. (I would say "die" but domain-specific languages tend to become undead -- unkillable beings whose origins are lost in the mists of time. How's that for a mixed metaphor? DSLs are restaurants that turn into vampires.)