Today I realized that when I blogged about how to use the KeywordQuery class, I forgot to mention how to specify the scope(s) you are querying.  You would think there would be a built-in property to set this, but there isn't.  I wanted to see how Microsoft was doing it so I used reflector and examined the notorious SearchResultsHiddenObject that the CoreResultsWebPart uses.  It in fact does what I expected.  It simply iterates through the list of scopes and appends each one to the keyword query string (i.e.: Scope:"Working Documents").  I was hoping there would be a more elegant way of doing this, but this appears to be the way.