"In physics,power is the rate at which work is performed or energy is converted."
Power equals work divided by time. So you get more power with less time.
This is, pardon the pun, a powerful metaphore. Hashtags or # plus a key word is a powerful formula for cataloging, idea jotting, event reminders, and just about anything you can use a "keyword" for when tagging.
For a longer description:http://www.techforluddites.com/2009/02/the-twitter-hash-tag-what-is-it-and-how-do-you-use-it.html
Where do you use it?
Well, it is a serreptitious use of twitter that has been applied to everything from geekpoles to conference notes. Simply tweet with a #keyterm and anyone can use the Search function of twitter to read what you are doing, thinking, working on, listening to, planning, etc.
A very cheap universal SMS or Short Message Server since twitter is free and all those using it are already text friendly. Those who aren't can still get a free account and search with a web browser on their PC or Mac.
Smart. Very. Advertising and spam have even hacked into the Hashtag power.
Now, remember that this is public, and tweets can be "found again" using new time warp functions. Keep it clean, keep it professional, and most of all keep it useful.
How do you know to search for a #tag on twitter? Easy enough. Most conferences, pamphlets, and advertisements tell you the hashtag or keyword to search for.
Also, you can random search for things you think others might be talking about. A common trend is a #moviename or #celebrityname EX: #AliceinWonderland or #JonnyDepp
If you are a researcher, its a little sloppy and on the qualitative side, but if you are tech admin and trying to see where the wind is blowing today, you can learn a lot from your friends out there. If you work with a group on a particular software, you can all # your comments on issues and solutions with the software name. What if another organization that uses the same software hashtags their issues and solutions. FAQ on the move with more info as the collaborative group grows.
There are many more things I can think of to use the #tag function for, but I think what is most important is the realization that there is power in "mashing up" many of our social networking tools for faster solutions or easier lives.
So, what will you #tag?