Todoist.com is hosted on one of world's largest, most trusted and most secure hosts - Amazon Web Services who, in addition to our secure structure also have the industry's best security measurements. You can read detailed information about it here: http://aws.amazon.com/security/
In terms of seeing todoist.com in your search results of your email address, no I do not believe so. Google search results are personalized to you. Google takes information known about you and gives you results based on what they think you want to see.
Also, the results should just be todoist.com, which does not give anyone the ability to access your account. If someone else clicked on that search result they would be directed to todoist.com homepage, not your account. They would need your account information to access it, which they are not able to do.
So I hope that clears up your worries :)
I'd like to agree with Brendon on this one -- I, too have seen some interesting search results, but anytime I've seen something in a search result that was "personal" to me, I've been able to prove to myself that it's just a matter of being logged in via Google and that no one is seeing things they shouldn't.
Thank you, Todoist for the great answer to this otherwise unsettling question...