My rule of thumb is to use no more than two dashes in a keyword targetting domain name. I agree that a domain name with no dashes is best - but I prefer a .com with a dash to a .net, .org or .info But in a highly competitive niche, choosing a name with dashes may be the only option and the best way to go - unless you want to start paying silly money to somebody who has the best option of a .com without dashes.