We don't actually store usernames and passwords. We're all OAuth, all the time, and you're welcome to revoke access whenever you like. We'll also delete all of your data as soon as possible when you ask us to.
Even if that is the case, I might be more comfortable using Greplin if I knew more about your security practices. What procedures are in place to prevent my emails from being stolen?
Edit: I hate being the one to criticize an incredible idea that is the result of hard work. I feel obligated to add that I want to use Greplin and I probably will use it for Facebook and Twitter. (Facebook's built-in search is useless.) I really hope there is a way that I can use this for email too.