Multisites Can Be Easy
Hey, folks, just a quick note about Drupal multisites. I’ve put up 6 sites for a client on a shared hosting situation. 5 of them are using the same database with prefixes. The first one was tough, in fact it seemed impossible. Then I read a post that said, “with the settings.php file and directory set up per the installation instructions, just park the additional domains.” That works like a charm.
I think it probably gets more difficult if you are running a dedicated server, but most of us aren’t. At the end of this brief story, http://linesanddezigns.com/node/30, I have the name of the host. I am also running 4 sites, as a multisite with separate databases, with the same host for this and other sites.
Like most hosts, they don't know what to do when you first set up a multisite installation but they are wiser now...I am too.

Multisites
I agree adale. I host 6 sites on a Bluehost shared account. Although it took a little time, and the guys in support didnt know how to get it done, I was able to set up all 6 sites with only one codebase. Its as easy as 'parking the domains.' If the domains are 'add-ons' it will not work.
I recommend separate databases for the upgrade process. It just makes it cleaner and easier to manage.
Follow these instructions and be sure to park your domains.
http://www.cmsproducer.com/Drupal-Multi-site-Hosting-Multiple-Domains-Mi...
http://jessecravens.com
Be sure to read the ToS
yes, setting up multisite installs are easy, especially with a host using cPanel, but just be sure to read the hosts ToS.
I was recently looking for a new US based host, and was just about to sign up with SiteGround, as they were large, provided the service and features that I needed, and ran cPanel. However, when I looked closely at their ToS, they do not allow parked domains to be used in this way.
I asked the sales rep, and she confirmed that if any content differed from the primary domain, and the parked domain, this would be against the ToS, even though no redirects were being used.
That wasn't a problem for me at all.
My host was happy to help and welcomes everyone to do the same.
Dale Dahlgren
Chief Conceptologist
www.linesanddezigns.com
www.head-bone.com
www.imarketingreport.com
www.oldguysonwheels.com
Multisite in a subdirectory
This has all been very helpful. I've been trying to do this with add-on domains and it hasn't been working well.
My problem is that I need to have my Drupal instance in a subdirectory. (/home/mydomain/public_html/drupal/) Can I use parked domains to do multisite this way? Is there a way I can redirect the new domain from the root to a subdirectory?