Four-square does look nicer to me, but it is not a big difference, because the words' individual meaning is not important. You could say that "foursquare" is s

Four-square does look nicer to me, but it is not a big difference, because the words' individual meaning is not important. You could say that "foursquare" is simply a new word, and in english text about that company, you would write about "Foursquare", not "Four Square". On the other hand, experts-exchange is much better than expertsexchange, because the two words carry own meaning---you would not try to create such a word in english but write "Experts' Exchange". Therefore, I believe that these words should be separated. The standard way to separate words in domain names is the hyphen.