If someone has a recommendation on the best method of configuring this for multiple domains (not subdomains) on a cloud host, I'd appreciate the pointer.
In this case, I mean not shared web hosting in the VPS sense (one server, many customer sites) but web farm or web cluster (your site on many servers).
Sorry about the hijack, but you're not on Rackspace, are you? Wordpress sites there have been getting hacked quite a bit lately, it looks like they have a security issue.
I use this exact method (and a subdirectory, not a subdomain install) to run multiple domains off on a WP 3.0 installation on cheap, shared, GoDaddy hosting. No apache config editing whatsoever.
I haven't tested this with 3.0, but I had a dedicated IP for my WPMU installation. If the site is configured in the WPMU panel, it would work, without any Apache config needed.
Our startup runs on WP3 and the ability to allow multiple domains. Feel free to email me at eiso@tyba.com or add me on Skype: eisokant. I think I can give you some pointers.
I've found this: http://blog.mixu.net/2010/05/17/setting-up-multisite-wordpre...
Which references this: http://www.interconnectit.com/840/wordpress-3-0-multisite-wi...
These assume you can edit your Apache conf, and many cloud hosts don't support that.