I was curious about the "More people now speak Klingon than Esperanto" thing, but from what I can tell it's emphatically not true. The number of fluent Esperantists is somewhere in the tens or hundreds of thousands, whereas the number of fluent speakers of Klingon is closer to a few dozen.
Here are some sources, including a particularly cool 2009 Salon article on Klingon, Esperanto and conlangs in general:
Thanks for doing the legwork-- when you put it like that, yeah, it's pretty obviously wrong. I think where I ultimately got that from was a claim by Guinness that Klingon was the most widely spoken fictional language, which someone took to mean constructed language, and it kind of snowballed. Oops.
Here are some sources, including a particularly cool 2009 Salon article on Klingon, Esperanto and conlangs in general:
http://www.salon.com/2009/06/03/invented_languages/
http://en.wikipedia.org/wiki/Esperanto
http://en.wikipedia.org/wiki/Klingon_language
http://answers.yahoo.com/question/index?qid=20080228012811AA...