This link: http://www.hahnlibrary.net/libraries/formgenre.html confirms that it is appropriate for libraries following Library of Congress’ cataloging guidelines to code form & genre headings in the format 655 _0 Heading. rather than the old method of coding them as topical headings (650 _0 Heading.)
The 655 marc tag for genre denotes what the work IS, rather than what the work is ABOUT. Anytime a Library of Congress Subject heading is used in this way it should be input in a 655 tag. However, that being said, some library software packages do not enable the cataloguer to use 655 tags and have them be searchable. This was a problem for our library, but the software has been updated and we now use 655 genre terms on a regular basis.
Also of interest, are the Guidelines for the usage of moving image LC/genre form headings.
It is interesting to note that the excellent source we use for copy cataloguing, BookWhere rates the cataloguing copy with a score. However, no points are given for information in 655 tags in BookWhere. They only rate 650 tags. Hopefully this will soon change…