Russell Beattie has a post entitled Spotlight Comments are the Perfect Spot for Tags! where he writes

I read just about every sentence of the Ars Technica overview of OSX Tiger and learned a lot, especially the parts where the author drones on about OSX's support for meta-data in the filesystem. I originally thought the ability to add arbitrary meta data to any file or folder was an interesting capability, albeit not particularly useful in day-to-day activities. But then I was just playing around and saw the Spotlight Comments field that's now included at the very top of a file or folder's Info box and I grokked it! Now that there's actually an easy way to both add and to search for meta-data on files and folders, then there's actually a reason to put it in! But not just any meta-data... What's the newest and coolest type of meta-data out there? Yep, tags! And the comments fields is perfect for this!

Obviously nothing has changed in terms of the UI or search functionality, just the way I think about meta data. Before I may have ignored an arbitray field like "comments" even if I could search on it (haven't I been able to do something similar in Windows?). But now that I "get" tagging, I know that this isn't the place for long-winded description of the file or folder, just keywords that I can use to refer to it later. Or if those files are shared on the network, others can use these tags to find the files as well. Fantastic!

This sounds like a classic example of "When you have a hammer, everything looks like a nail". One of the interesting things about the rush to embrace tagging by many folks is the refusal to look at the success of tagging in context. Specifically, how did successful systems like del.icio.us get around the Metacrap problem which plague all attempts to create metadata systems? I see two aspects of the way del.icio.us applied tagging which I believe were key to it becoming a successful system.

1. Tagging is the only organizational mechanism: In del.icio.us, the only way to organize your data is to apply tags to it. This basically forces users to tag their data if they want to use the service otherwise it quickly becomes difficult to find anything.

2. It's about the folksonomy: What really distinguishes services like del.icio.us from various bookmarks sites that have existed since I was in college is that users can browse each other's data based on their metadata. The fact that del.icio.us is about sharing data encourages users to bookmark sites more than they typically do and to apply tags to the data so that others may find the links.

Neither of the above applies when applying tags to files on your hard drive. My personal opinion is that applying tagging to the file system is applying an idea that works in one context in another without understanding why it worked in the first place.