rel="logo" is a standard I proposed over a year ago as a way to deliver up to date SVG logos. It was rejected by Microformats for it's similarity to rel="icon". I disagree that logos and icons should have the same use, but I'd like to resurrect/rebuild the idea and attempt to make it more useful.
At the moment, there is no good way to deliver and find current vector logos. Site like Brands of the World don't do a great job, and not every site has a brand guidelines page.
So, is an idea like rel="logo" useful? Could it be improved? Would you use it on your site?