Atlassian Codegeist has never been so exciting with many great submissions, one of them is Jitter written by Viðar Svansson.
Jitter is a plugin that brings microblogging features to JIRA by adding social walls to projects and user profiles. It also ships with a gadget so you can include it in your JIRA dashboard or even on your Confluence space.
It sports some great features borrowed from Twitter, such as automatically linking URLs, users, hashtags in posts along with integration with JIRA issues by automatically linking issue keys. The plugin also supports searching using the new powerful Active Objects plugin for JIRA 4.3. Head over to the Plugin Exchange to have a closer look at Jitter for JIRA.