I don't know about external facing and 'most web sites use SharePoint' but SharePoint is mainly used in conjunction with other midsize/enterprise MS applications such as Exchange, SQLServer and other MS products, including SSO integration with Active Directory. I've yet to see it used as standalone with only MS SQLServer. If you want to use a CMS without having the need to use any other enterprise, or midsize, MS apps, it's expensive to deploy as you'll need to deploy on Windows. On top of that, the recent version Foundation 2010 is a PAIN IN THE *SS to deploy and maintain with any SQL Express version. Don't even think about developing it further on the Foundation 2010. Buying MS SQLServer just for the sake of SharePoint only is not worthwhile as that cost is even higher. Furthermore, SharePoint 2010, even the free version Foundation, is very hardware demanding. Simply put, if your company currently using any MS products, Exchange, SQLServer, etc. and is midsize+, then it maybe justifiable to use SharePoint, not just the free version. Else, if you just need a CMS that's the lowest TCO and easier to maintain, stick w/ PHP and Open Source, IMO.