My collegea Mart wrote an article about the last modified date of a WSS site. The SPSite class has a property called LastItemModifiedDate returning the last date of modified content. If the method GetSubwebsForCurrentUser is used this property does not contain a value when used for the root web. The following definition of both members is found in the MSDN library:
LastItemModifiedDate
property of the SPList class gets the date and time that an item, field, or property of the list was last modified.
LastContentModifiedDate
property of the SPSite class gets in Coordinated Universal Time (UTC) the date and time when the content of the site was last changed.
Mart and Tariq give us a solution for this problem by getting the SPVirtualServerCollection of the SPGlobalAdmin and then looping through the Sites collection per SPVirtualServer. The property LastContentModifiedData is filled in. :)
Thanks guys! I'm gonna need this in one of my next projects
http://blogs.tamtam.nl/mart/SharePointTipLastItemModifiedDateAndLastContentModifiedDate.aspx