Does it matter if you have a single site with multiple domain names ? I know this is common. I am just curious if this has an effect on your search engine ranking because of content duplication.
I do this on most every niche I have sites for and it works well. I would recommend submitting a sitemap index when using multiple domain names.
Because the power of multiple domains works when targeting multiple highly competitive keyword phrases. You can create specific meta keywords, title and meta descriptions for each domain name parked over the same host. Sweet!!!