Communication is a key ingredient in the freemium business. It is important to know when to communicate with your customers, and what is the right venue to do so.
Typically, email is only used at the two ends of the freemium cycle, on account creation to confirm the details and to make sure the credentials supplied are legit, and upon account termination to make sure that the person really intends to terminate the agreement.
In between those two points, typically the website is the way to communicate, unless you plan on some drastic move that will potentially affect your users in a negative way. In that case an email won’t hurt.
The reason to keep email communication down to a minimum is because it is intrusive and it tends to be ignored. When a users visits your website in the normal course of their day they are much more receptive to communication from you. Some websites (notably facebook and twitter) flaunt this and I think the only reason they’re getting away with it is because they’re doing it in the name of your ‘friends’ (I use the term loosely ;) ). If the emails would be system messages not directly related to communications with your peers then they would likely be ignored or cause aggravation (see ‘respect’).
A better way for important stuff is to place it in a ‘sleeper’, a message box that catches the user the first time they log in to the site again.
Use blogs for open ended communications to your most interested users, and a ‘news’ section that is kept up to date for those at intermediate levels of interest.
Keep the tone professional, say what you have to say and don’t insult your users intelligence with corporate double speak, especially not when you are taking something away, users are not stupid and they’ll take you to the cleaners if you insult them in this way.
Clarity is key and an unclear message is worse than none at all.