I was interested to see the announcement on Flickr of a new syntax called machine tags (via a story on machine tags from Programmable Web).
Machine tags are a way to provide structured information within a tagging structure. It takes the traditional tagging format (just words) and adds a little structure of the form "namespace:property=value".
I like machine tags; they map cleanly into RDF. I'll be interested to see how the rel=tag microformat will grow or adapt to this new structure. My guess is that there will be some resistance.