My life tagging files

Metadata seems to be the next big thing for filesystems. Apple released OS X v10.4 with the “cool” Spotlight that lets you search your hard drive for files and contents. Windows Vista will feature something similar.
The cool thing of SpotLight is certainly the possibility of search for words within the documents (or emails) and it is damn fast if you consider that it is searching your entire hard drive.
Google Desktop is another.

Recently I installed a plug-in for Mail.app called MailTags that many think is awesome.
I installed it because I wanted to check how cool it is (I have read more than once and on different sites how cool it is).
I have to say that it has some really neat features that let you add comments to emails, keywords and associate email to specific projects. A new feature that I have to say is really cool is the ability to integrate with iCal (the native OS X calendar). When you receive an email you can assign a due date and it will add it to iCal automatically. This is just great, I have to say.
I tried to tag a few emails, I tried to add metadata to a few files here and there… What I don’t understand is the final use of all this metadata. If I have to spend let’s say 5 minutes for each email or file that I receive to tag it with the project, a task or a few comments, then why not simply archive it in the appropriate directory or folder?
I don’t see this GREAT advantage from tagging files and e-mails. Looks a lot like archiving.

I am wondering what is people doing with their tags and how they use them.