This looks like it might be very similar to something that's been bouncing around in my head for quite a while - I greatly look forward to trying it out!
Any chance you'd consider working with the Mailplane[1] author to get it integrated? That's my Gmail client of choice, and Ruben has integrated other tools like Rapportive, so I'd hope that something could be worked out.
I've long since admired Mailplane and it would be great to do something with Ruben - I didn't realize that he was open to collaboration. Will get in touch.
And if you have any thoughts about what you like, don't like, or would love to see and want to discuss it more deeply, I'd love to go into it :) Just say hi at andym@activeinboxhq.com (or the community forum: www.getsatisfaction.com/activeinbox)... or here at HN of course!
Any chance you'd consider working with the Mailplane[1] author to get it integrated? That's my Gmail client of choice, and Ruben has integrated other tools like Rapportive, so I'd hope that something could be worked out.
[1]: http://mailplaneapp.com/