Joe Johnson: Sorry for the delay getting back to you. If you're looking to launch a slew of affiliate or Adsense driven sites than XSitepro is a good solution. However if you're looking to grow a community or authority site you will need add a slew of web applications from here and there to really grow your site without you doing all the work.
Here are some of my top Content Management Solutions (CMS):
Commercial
SubDreamer - Probably my favorite for the price, support, plugins and SEO
Semiologic - WordPress HyBrid
Open Source
Joomla
Drupal
WebGui
DragonFly
Paula: No there is no limitation as to how big an XSitepro site can get. It's just that it will take you much longer to build content up on a non community driven platform. That is why blog, hybrid blog CMS's and standard CMS's have really taken off the past couple of years or so. More content = more Ad/Affiliate revenue