Managing email programatically in particular for me is a nightmare, sendgrid is an awesome service, but processing incoming email should be much easier. (I have yet to try lampson)
But the UI also irked me, it was far far to bloated with features I didnt care about (replay), when the thing that I care about was it being as fast and responsive as gmail, which it wasnt close to.
It's just a noisy mess, poorly designed, with a lot of weird design decisions and exotic patterns that only added to the noise.
It starts with a way to complex proposition. Google basically created the entire vision instead of the basic core functionality and then expanded on that, optimizing in the detail rather than for the big shows.
Etherpad started the right way. It started very lean with a basic principle that then evolved with time, slowly. And now it got bought.
Another problem with Google Wave is that it's inherently centralized. They transform the insert/delete operations so they can be applied out of order and still converge on the same document state. Unfortunately, the method they use for this requires a central server to maintain causal ordering of the operations. There are ways of doing this that don't require a central server, which could be handy.
But have you looked at it recently? I've been using Wave to manage most of my project-related communications (with one or two partners), and it's fantastic. Like Etherpad, but a lot more powerful. And fyi, the Etherpad team is now part of the Google Wave team.
They've opened it up now so that you can design a better interface if you wish to. They've also opened it up to anyone with an email address now, and expanded on the robots and gadgets.
Now I don't use Wave that much because I don't often need the collaboration that it offers. However, if they could integrate Wave and Gmail, it would be immensely useful, especially the gadgets and robots.
Is there an available solution for the reverse of SendGrid? Basically a service which would receive your emails and then post to a url on your application.