Hosting multiple WordPress sites with WordPress Multisite and Domain Mapping

I use WordPress to run my blog. I recently had the need to run another site and wanted to also use WordPress as my CMS. However, I don't want to run another installation of WordPress if I don't have to. I followed the directions on here to create enable WordPress Multisite, and followed the directions on here to make use of a different domain name for my second site. Basically,

• backup my WordPress database and WordPress directory first
• enable WordPress Multisite via wp-config.php
• disable all WordPress plugins
• follow the install options on my WordPress site
• re-enable my WordPress plugins
• install the WordPress MU Domain Mapping plugin
• continue with instructions here

Some things specific to my setup:

• sub-domain was enabled by default from my previous WordPress installation; I had to add the CNAME *blog.mydomain.com to my Host DNS configuration, where blog.mydomain.com is my current WordPress site. I also had to add the line ServerAlias blog.mydomain.com =*.blog.domain.com to my VirtualHost setup my Apache web server configuration.
• mapped my WordPress site 2 from site2.blog.mydomain.com to site2.mydomain.com, where site2 is the name of my new WordPress site.

Now I am able to host multiple WordPress sites from the same WordPress installation. What is the down side? I have to manage plugins and themes that are available for each of the site…