Bad move, Lightning! Rated 2 out of 5 stars
Do not like the waste of screen space below my folders, which used to be utilized by the calendar. I don't want to have to lose the mail view, just to see my calendar. If I wanted that, I'd already be using Sunbird, in a separate window.
Even on a wide-screen at 1440x900, the new 'Today' pane takes way too much room from the message list, especially since I use the Show Address add-on so I can see the real sender when sifting out spam.
My only option is to widen the T-bird window and cover up 3 vertical rows of shortcuts on my desktop that I use all the time, or go back to the previous version. Unfortunately, I don't see any option in the Update Notifier add-on to ignore Lightning updates. I'm hoping the developers give us back the option to keep the old display. HINT HINT