Rated 5 out of 5 stars
Overall I love the look. The button icons are beautifully drawn and the choice of colour is mostly very attractive.
However, I did find a couple of things a bit distracting / tiring after while which tempted me into making my own small modifications. Specifically I found the blue folders just a little too bright, and the scrollbars need softening. Also, I prefer Today|Tomorrow|Soon without text shadow. But apart from those minor quibbles - it's a great looking GUI!<br>
Edit (14 Oct 11): Thanks for the update Alfred (see developer's reply below) with all the changes I suggested. Nautipolis is almost perfect (to my taste) now! Now if only I could persuade you to reconsider modernizing those very retro folder icons :D.
I have just released 1.8.77 with these changes incorporated: toned down colors of folders and thread pane icons, improved scrollbars, and shadow removed from Today|Tomorrow|Soon.