I learned about What the Hashtag?! (http://wthashtag.com/Main_Page) from Andrea Meyer of Working Knowledge (http://workingknowledge.com/. Andrea works a lot with Twitter and her expertise is valued by many companies.
I tested What the Hashtag?! and wanted to show one way I found it useful. First, from the website What the Hashtag?! they describe their services as "a user-editable encyclopedia for hashtags found on Twitter."
If a hashtag is setup (I tested #health) for a topic, type it in and you will see a description for the hash tag, contributions the last seven days, top contributors, area to have a live conversation with folks on this specific hashtag and what makes me really excited, is a view transcript tab.
Click on it and you can get tweets for some time back. I went back one month for #health and received a transcript for 30 days worth of tweets on #health.
If there is not a hash tag setup for your purpose you can set one up. Here is an example of one I setup for some work I am doing. I wrote the hashtag, description and have promoted this tag on other listserv's and social media sites as the one to use for this year's Race Across America. (http://www.raceacrossamerica.org/).
Lastly, and this is also really exciting, What the Hashtag is a place to get the transcript from a conference, if it has been setup. As an example, the Association of Information Professionals (http://www.aiip.org/) is having their annual conference starting April 28, 2010 and has designated the official hashtag for the conference as #aiip10. Since this hashtag was not setup, I setup one up for the hashtag (#aiip10) for the AIIP 2010 Conference and described how the hashtag can be used on What the Hashtag. I can now type this hashtag into What the Hashtag and have a transcript from the entire conference. This could also be used to have live conversations during the conference, from anywhere, as long as an individual is registered on What the Hashtag. Here is how it looks now before the conference starts.
After I set the #aiip10 hashtag up, this is how it looks now. I tweet as lebird (http://twitter.com/lebird)and infoliteracy (http://twitter.com/InfoLiteracy) and they showed up about one hour after the tweet. You can also see the other tweets leading up to the conference.
I believe this is a valuable tool to have live conversations on a topic plus gain a transcript on #hashtags. Thanks Andrea for bringing this to our attention.