My understanding is that the Sharepoint Agent will allow you to restore individual documents from the Sharepoint environment. If you use the SQL agent or the Server Recovery product, you'll be forced to restore the entire environment to recover a single document.
I also believe that the agent will do this for both Sharepoint Portal Server, as well as WSS.
Last - the current version of the BE Sharepoint Agent will only work with Sharepoint Portal Server 2003 or 2001, and WSS V2. Portal Server 2007 and WSS V3 are expected to be supported sometime Q1 2007.
Someone please coprrect any of this if it's incorrect!
Thanks - Joe