Probably not enough.
Do you know when their birthdays are? Do you know how they heard about you? Do you know why they chose you over a competitor? Do you know how their experience with your product or service has been since they purchased?
You can never know enough about your customers, because the more you know, the better suited you are to serve them, to sell to them, and to create for them.
Track everything. When did they purchase, why did they purchase, when are they likely to purchase again? Keeping track of this type of information will make it easy for you to see trends and habits that have always been there. And once you have the information, put it in a place that makes it easy to view, search, and sort. The key to obtaining the information is the ability to use it. Just because its there does not mean that it helps you.
Give the information to your sales team so that they can offer them new products and services, or upgrades of the things that they already have.
Give it to your customer service department so they know exactly what is happening every time they pick up the phone to deal with an issue.
Give it to your marketing department so they know how to better position themselves to attract more of the same type of people.
The best companies know as much as they can about their customers. They are able to serve their needs before a customer even knows the need exists. They keep channels of communication open at all times, not just went they want to sell something. And the customer responds to this.
The more you know, the better position you will find yourself in. So start learning today.