However, to make it easier for me to keep the tags list somewhat clean, I've changed the settings a bit. Now you can add tags, but you can't create new ones. This is to cut down on duplicates and mispellings, primarily. I've created a tag called "no category" for you to use if you think I need to create a tag for a post.
One of the major drawbacks of LJ's tag feature is that you can't search two tags at once. For example, you can't search for posts tagged with both "united states" and "colleges"; if you wanted information on United States colleges you would have to search one or the other.
Another drawback is that you can only display the past 100 entries with any tags.
That's the reason behind tags with this sort of structure:
united states: education: higher education
It's ugly, but it does make it a lot easier to search past posts for specific types of information. It also keeps the popular categories (like "united states") from going over the 100 entries limit.
Generally, if there exists a more specific tag, I would prefer if you only used it and not the general tag, because I'll be going through and removing the general tag anyway. That means if you're asking about colleges in the united states, you should only use the "united states: education: higher education" tag and not any of the more general ones.
This is just a suggestion though. Don't feel like you can't tag posts if my anal retentiveness is too much for you! Keeping posts searchable is more important, so anything you do helps.