Personally, I have not bothered to learn Esperanto, mostly because while it's "marketed" as a beautiful and good-sounding language, it's not. And need for weird characters or the common ASCIIzation involving x's clearly doesn't make it any "cooler". Plus, if you need an "universal language", English is pretty commonly understood around the world.
Also, people who have studied Esperanto report that the "16 rules" are definitely not enough to learn all of the subtleties of the language.
An interesting factoid:
In America, [Esperanto's] most widespread application has been in wargames; when rehearsing European battles, the US Army used to designate Esperanto as the official language of the Aggressor Force.
- Wired Magazine, August 1996
Quite of an achievement from a language designed to promote world peace =)