What's great about hashtags.org is that clicking on a specific hashtag amongst those suggested will take you to a page that shows a graph of the hashtag's popularity over the past month (which wouldn't work for the term "rovio" we've been discussing over the last few weeks as it appears no one has used it in a hashtag).

Hashtags.org also provides a for the selected hashtag which is, by default, in Atom format (although it appears that if you change the URL from ending with messages.atom to messages.rss you'll get an RSS formatted feed).

There's a small problem if you want to do anything with this data in Excel: While will happily access a hashtags.org feed in either format, it appears Excel will not. And, of course, Excel reports the problem with a cryptic error message that requires you to go and find a log file that contains the error report. Argggh.

Another interesting Twitter search tool can be found at . The home page shows a tag cloud of the most popular words being used on Twitter (which refreshes every 20 seconds), and offers a search box that brings up a list of Tweets mentioning that topic and a graph showing the number of mentions over time.

Click on the graph or the link at the foot of the results and the next page will be dedicated to your search results and allow you to change the graph time window from the default six hours to either one day or three days.