Bool values are not indexed in MOSS
Have you found some problems indexing boolean values from lists?
I realized that as Yes/No crawled properties are based on the VariantType 11, it will be parsed as a 0 or -1 value; however Yes/No columns in SharePoint are stored as 0 or 1 values.
You can check some information in my previous entry
Just drop a comment if you have this type of problem. Maybe a quick solution would be to change the VariantType for an integer type or to create a custom control field...or just query for the negative logic (!= False)