I'll be blunt: Anything that promises me a "more enjoyable" inbox, and then advertises with cat pictures and what-do-we-do-for-lunch threads is missing the mark for me. I don't want more fluff in my inbox. I especially don't want anything that helps people "email faster". It's not productive, it just makes more noise. E-mail is a medium for half-baked thoughts quickly dashed off to put them on somebody else's plate.…
Don't be confused by the fun examples. Everyone likes cats (those are my actual cats) so we put them in the post, but you certainly can send more important emails :)