Note:- Before you follow any blog make sure to check that they are related to the version you are dealing with. Don't follow a blog if its for Beta version of SharePoint 2010 when you have released version.
If you want to create new SCOPES with FAST search, now you can create scope filter from GUI instead of creating them using Windows PowerShell.
From technet -
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Documented product changes implemented in the August 2010 Cumulative Update (CU) - http://technet.microsoft.com/office/ee748587.aspx. With the CU installed, the FAST Search Server 2010 for SharePoint scope filter is automatically generated based on the scope rules created by using the graphical user interface. Administrators no longer have to create the scope filter manually by using Windows PowerShell.
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Create and view search scopes (FAST Search Server 2010 for SharePoint) http://technet.microsoft.com/en-us/library/ff453895.aspx
One thing that is not clear from the above link is, creating scope rules based on content sources with FAST search. It's very easy to do with SharePoint 2007/2010 search - For "Scope Rule Type" you can select "Content Source" and then select your content source from the drop down list.
Now with FAST search on "Scope Rule Type" you won't see "Content Source" as one of the option to select, but it's part of "Property Query" with "Property Query" we can give codition for selecting content source "ContentSource = FileShare" (assuming that you already created a content source as FileShare).
Long story short with FAST search to access your Content source from a Metadata Property "ContentSource" which can be used to restrict or include results with Scope Rules.
