So far really like how you've put this together, quick to use, but flexible.
I run a small agency (me and 2 others) and the one thing I'd love to see in a tool like this would be a basic CRM.
Simple way to add contacts (imported from gmail like is already possible but adding outside of that as well).
Stores all emails against a contact.
Can add additional fields to a contact
Can add tasks against a contact
Can add notes and documents to a contact.
Might be a bit beyond what you're trying to do but so far I can't find one good, simple tasks / contact management tool.