Two modules, currently in development, look like they go halfway to an ideal solution. One by Jordan Willms uses the taxonomy to automatically create Technorati tags, but aren't tags at the system level, since you have to create the taxonomy terms manually through administer » categories. (That said, in the next release of the Bryght platform, we will include 'free-tagging', which automatically creates taxonomy terms 'on the fly' as you post.) Another module adds a box where you can type them in, but doesn't use the taxonomy. Of the two, the last one is closer to what you're thinking. Neither do b), but my guess is you wouldn't need it if the system automatically created the tags anyway.