If you don't mind hard-coding the filtering process, you can change the search algorithm to not include certain metadata types (like always ignoring camera model). If you are using SQL Server, it is especially easy because the logic is in the stored procedure gs_SearchGallery.
Otherwise, while I agree that modifying the UI to include an advanced search would be useful for some, it is not a top priority, and therefore unlikely to appear before 2013.
Roger Martin
Creator and Lead Developer of Gallery Server Pro