Most of the time it doesn't come off as intelligent. People know what the high falutin words mean. They just don't use them because it's unnecessary, and sounds rather stupid.
People who use big words tend to be people trying to prove to others that that are intelligent, and usually are trying to prove that they are more intelligent than the people they are talking to.
Generally though, they tend to be less intelligent and just come across as poncy and stuck up.
Also, intelligence with regards to big words etc, is no use if its not backed up with a degree of common sense.
