Since Office SharePoint Server 2007 and Search Server 2008 best bets are search related you would think that they are Shared Service Provider specific, but this is not the way to think about them. Yes, the actual best bets that are defined in a SharePoint site collection are stored in the SSP database, the scope of them are a site collection. This means that if you define best bets in one site collection you cannot use the same entries in another site collection. If you wanted the same best bets you would have to enter the same best bets for each site collection. This is why you go to the actual site settings page to enter the keywords and not the SSP administration site.

These Technet and Office online articles do not specifically go over what the scope is for best bets they mostly go over how to enter the keywords.

 

Add, edit, and delete keyword Best Bets

 

Add keyword terms with Best Bets (Office SharePoint Server)

 

You can however return best bets from one site collection in the search center of another site collection by changing the site collection's search settings page (/_layouts/enhancedsearch.aspx).