I have a multisite install running 3 sites. It seems that anytime you to domain.com/site1/ or domain.com/site1/page1, it automatically redirects to http://www.domain.com
I am not sure if this is a DNS issue or just the way the MultiSite was configured or what. I have verified that the htaccess file is still just the basic htaccess.
Also, the "domain" under Network Admin > Site is set to have the www in it.
Also, this is in the wp-config file:
define( 'DOMAIN_CURRENT_SITE', 'www.thesummitonline.com' );