From a branding point of view the bad thing is that when you say the name of the domain over the phone you always have to say bla-hyphen-bla.com which is a pain.
Buying the domain is the least expensive thing you can do. Building a brand and investing in launching a site on the other hand can be one of the most expensive things you can do. An amazing site can do well in spite of a bad domain name (example: pinterest!) but a well known domain doesn't guarantee a great website or brand.
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[ 3.0 ms ] story [ 27.1 ms ] threadA hyphen screams unprofessional to me. @michaelpinto has covered most of the rest.