Rated 5 out of 5 stars
Lightning is a phantastic add-on for Thunderbird. Thank you very much for writing it. I am using it with the Calendar Tweaks add-on to have catagorized events completely colored to enhance readablity.
Only weakness that I found so far: Events that span more than one day are displayed in month view as if they were single events. I.e. a three days event may be shown on Monday as the first event of the day, on Tuesday as the third event, and on Wednesday as the first again. So the event looks like three events totally unrelated to each other. I hope this gets fixed soon.
EDIT: Just found an entry in bugzilla for this: 256588, reported in 2004. Well, so much for the hope for a quick fix :-(