Communicate. Communicate. Communicate.
We always send out information to our clients, when appropriate. Things such as new promo's, press releases, notifications of system upgrades that may effect their service, etc.
Personally, I would rather be informed than be caught by surprise. I would rather be told about a promo that I might be interested in than happen to run across it on a board somewhere and then confront my hosting provider.
Keeping lines of communication open will help build a "relationship" with your clients.
If you are worried that they may be "bothered" by some of your communications you can always create a series of mailing lists and then give them the ability to subscribe/unsubscribe to the notifications that don't care about.
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