Hashtags are a useful technique within twitter, and the hashtags.org site was a great collaboration site for tracking hashtags. However the site has not been updating since July because of problems with Twitter’s XMPP service.
An alternative to Hashtags.org is Twemes.com the site aggregates hashtags but also enables you to install a widget within a blog post for a specific hashtag.
Check out this Tweme for a recent Forrester event for example.
What’s really nice about Twemes is that you can customize the widget, showing anywhere from 1-10 tweets featuring a hashtag, and the site provides an rss feed for hashtags.
Update 3/7/09: Hashtags.org is up and working again.