[dpritchett]

Sharepoint 3.0 was free to anyone with a Windows Server 2003 license. Once you build out that infrastructure a bit the marginal costs to upgrade into MOSS (SharePoint 2007/2010) start to look ok.

I personally prefer more socially focused solutions (e.g. Jive) but SharePoint is making huge strides as both a collaboration backbone and as a document management platform.

Some Fortune 500 companies are now building new intranet apps around SharePoint rather than standalone. There are a number of off the shelf solutions available as SharePoint "web parts".