I may have different interest that some people, as I'm planning to bitzi to extract metadata for use in my p2p app's catalog of files.

• Guess the mime-type and use that rather than "tag.image.format", or "tag.video.format"
• AVI tags (see this list of possible tags. Looks like I need to write a command line util like id3v2 to get more people using this. I would be nice if my opensource set top box could organize stuff as well as the iTunes clones).
• Output RDF triples on the client side. The catalog schema in Mnet is based on RDF. My python wrapper does this already, but not as well as it could
• Adding a BitSociety tag from the command line

For the website itself:

• RSS list of BitSociety files (this was suggested by someone else). Hopefully you could employ a) staticly writing the RSS feed once per update, b) some restriction that would disallow clients that didn't use ETags or Last-Modified-Date.