Showstopper 11/6 '14
I got an invite to use Google's new Inbox thingy the other day. If you haven't seen it, it's a layer over Gmail that bundles messages into thematic groups and lets you deal with them in large batches.
It's an interesting notion, though it doesn't exactly match the way I've been using Gmail (which is to use the Priority Inbox, and strive to keep "Important and Unread" clear while letting stuff accumulate in the rest of the Inbox). Still, that's something that could be managed over time.
The showstopper I encountered was when actually composing a message. It doesn't include the per-sender-address signatures defined in Gmail. I waited literally years for Google to add that feature, I'm not going to give it up now.
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Leave feedback! I'm definitely pointing out missing things as I go -- for example, I couldn't mail to a a contacts group. Very bad; I had to pull up Gmail to send mail and it's going to happen on a regular basis. I left feedback. There was something else, but it slips my mind at the moment.
Generally, though, it fits my use patterns pretty well. I can certainly see it won't for others. I love the snooze feature with a great love, though; much like "don't show this to me until X" in todo list managers, which has become an essential feature to me (and my sanity.)
Ultimately I think it's for people who're already using their inbox as a todo list, which I do.