Fantastic responsiveness, great look Rated 5 out of 5 stars
I emailed the author of Walnut2 about a (minor) problem with the background--some fields were shifted when selecting multiple emails. He had it fixed and ready to test within six hours, and had the change (after I told him that the problem was fixed on my computer) uploaded in a few days.
That's really amazing. In addition, the look of this background is very clean and makes T-bird an even better email program.