>The functional distinction between a folder name and a tag is really non-existent, except that tags have a lot of additional potential features such as: files can be in multiple tags
This isn't a very good example as with links files can be in multiple directories.
>[cut]tags can be applied to non-file data (e.g. people, or rather their contact / identity information), etc.
In a "Plan9" like organisation, everything is a file so the difference between tags and directory&links would be smaller..
I'm nitpicking, but anyway kudos for using tags! I think that this is a bold move which can be great for the users and I hope that it will succeed, I'm only a bit worried about the performance cost of using tags instead of directories (directories have already a big cost when using HDD as they "hide" the block's position on the disk: http://simula.no/research/nd/publications/Simula.ND.399/s... )