Star Trek has money, like gold pressed latinum, but the rest of the time, they revert to a barter system; not exactly utopian economics.
At Sisko's creole restaurant on Earth, what does his father pay the waiters? How does a person get a table? Who gets all of the Picard family wine? Just because they don't use "money", doesn't mean there isn't an exchange of value.
What do you think a person from the 1800's would think of a credit card? He'll probably think that we abolished money.
This discussion is held at many sci-fi conventions and the consensus always returns to the fact that in order for Star Trek to sustain it's economic model, there must exist an unseen SLAVE class doing all work. (Which was addressed when Voyager showed the Doctor's hologram brethren working in dilithium mines.)
http://capitalismmagazine.com/2002/08/franciscos-money-speech/