Scott Morrison sends word that MailTags, the Mail plugin that lets you both tag your emails and connect them directly up to iCal, has hit 2.1.1. The 2.1 release came a few days ago, and introduced incoming reply tagging-- whenever you sent out a message with tags on it, the reply that came back automatically received the same tags-- and the 2.1.1 update improves that feature. You can now tag an outgoing message as "expect reply," and MailTags can notify you through Growl and with highlighting that the reply has arrived.
The release also includes an example AppleScript that lets you use a "killed" tag to mark a message and any incoming replies to it as read-- if a thread has ceased to be important to you, you can ignore it completely. Bugfixes involving iCal interaction have also been implemented, and a column sizing interface improvement has been added.
The 2.1.1 update is a maintenance update and available for free to MailTags users over at the website. If you haven't bought the plugin yet, you can get it here for $29.95.