one domain with several temporary blogs & sql DBs

Hi Guys.
has anyone created multiple SQL databases and then had several wp installs for each SQL?
I want to provide my clients with a temp. sites, without purchasing extra domains. ie. http://www.mysite.com/clients_site (private viewing, log in req.)
I have read there maybe problems with themes and plugins when you install a separate wp install in a sub directory. ie. public_html/clients_site
I would also have an install in the root directory.
I have found the docs on it but was just asking if any one has already done this.

Thanks in advance