Sorry to have to be negative about Mobysaurus. I simply find that it throws up far too many supposed synonyms, many of them bearing only the faintest link to the initial word.
In principle it is a good idea, but it really needs to have the synonyms categorized in some way, perhaps also using some scoring method. The trouble with all thesauruses (or should that be thesauri?) is that they only use the information by one word given by the user, which cannot be qualified. If the user could also give a second or maybe a third word to help qualify the initial word, then the words that score highly for both the initial and the auxialliary words would be at the top of the list.