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I have added the Technology metadata column to the Search Facets web part on this page http://www.wssdemo.com/Search/Pages/results.aspx?k=sharepoint

 

You may notice that it doesn't work to well with multi-select lookups.

 

If Content Types are used correctly, they would be an ideal candidate for filtering search results. The problem is that adding this field to the web part lists a number of system content types that you would not want to be displayed.

It would be nice if there was another attribute in the <Column> element to specify the include or exclude metadata values from this column (you will understand what I mean when you configure the web part).