We've just released JIRA Client 2.2 Beta 1, featuring support for JIRA 4.1, the newest version of Atlassian's issue tracker.
Some UI improvements and bug fixes are also there. Upgrade is required if you're switching to JIRA 4.1, otherwise feel free to try it out.

• The complete release notes are at http://almworks.com/news/2010-04-jiraclient-2-2-beta.html
• The change log is at http://almworks.com/jiraclient/changelog.html
• Download the beta at http://almworks.com/jiraclient/prerelease.html

-- Pavel, ALM Works