I was just talking to a friend who was asking about how to find the right tone for communications to fans/users/consumers via text (blog posts, emails, forum messages). Here’s my formula, for what it’s worth.
Write the first draft in the exuberant tone that you want it to sound like. Make it as upbeat and over the top as you are really feeling. Let your own enthusiasm come through. Be honest here, don’t try to add marketing language. If you were telling your buddy over beers about the cool new project you’re working on, how would that sound?
Take your first draft and cut out half the exuberance. Remove half of the exclamation points, half of the statements like "we’re so excited!", and so on.
When you write it the first draft (if you’re being honest), you’re setting the structure. But when you revise for the second draft, you’re adding presentation. Online the dividing line between enthusiasm and marketing babble is a thin one. Too much excitement and you’re a cheerleader. Not enough and you’re just "doing your job".
The two step process above has worked well for me over the years, but your mileage may vary.