FAST Search is an Add on to the exisiting SharePoint Search.
Standard SharePoint Search Offers the following
* best bets
* facets
* related popular searches etc.,
And FAST Search provides the following Add on's:
* Item counts on the facets
* Visual previews of content
* User contexts
* Extend the core results webpart (uses XSL)
* XRank can be used for soft boost of search resutls
