I've had a number of startups (OrderAhead, Instacart) email me shortly after I've signed up with a 'personalized' message. I've had issues or questions so I've followed up with them straight away - only to get no reply.
That, in a nutshell, is a perfect way to destroy retention. If you're going to do stuff like this, it's critical to follow through. My opinion of a company is strongly tied to how well and how quickly they respond to customer feedback.