For those of you who have experienced some confusion setting up Multiple Domains on your WordPress Website, the MultiDomain WordPress Plugin will save you some time and headache. MultiDomain is a simple plugin that allows a WordPress website owner, or their developer, to use multiple domains on the same website.
For instance, one of my new clients wanted to use three domains on his new website. Using MultiDomain allowed Vintage Race Car Sales, Historic Car Sales, and Historic Car Collection to use the same WordPress theme (though separate themes can be used) & the same WordPress content in the same database.
While it might not have all the options of a WordPress MU setup, it 95% less of the headache that setting up WordPress MU on a shared hosting plan for a site that is an Addon Domain. Also, before you make the decision to use multiple domain names, make sure you read up on Duplicate Content to learn the do’s and don’ts regarding multiple domains.