Directly emailing a customer in a way that appears personalized is a great way to solicit feedback. Don't expect to generate digestible information with this method, but you will get a strong pulse on your business plus it builds relationships. The methods described here are best for capturing feedback from users who stopped using your SaaS product. You can find the accompanying blog post here: http://blog.listenloop.com/cheat-sheet-for-user-feedback-surveys