From a SEO standpoint I would like to use 3 keywords in my URL. The dot com of these 3 keywords is taken and parked. From a marketing standpoint which should I use? mythreewords.net -or- my-three-words.com
mythreewords.net if you're creating a site for people to visit, my-three-words.com if you're creating a site for bots.
definitely mythreewords.net, I've never had problems with hyphen .com but if I have the choice of a shorter and intact word for .net, I'll definitely stick with the slicker mythreewords.net.
1 dash should be your limit, and 0 dashes should be your first choice. Looks more professional and easily to relay through word of mouth.
I think mythreewords.net is a lot better. When you use dashes you are going for SE ranking. My rule of thumb is to build a site for the people, not the search engines.