The default value is submit, meaning any button in a form can submit the form. Use type="button" for anything that doesn't submit the form and type="submit" for those that do.

<button type="submit">Save changes</button>
<button type="button">Cancel</button>

For actions that require a <button> and are not in a form, use the type="button".

<button class="dismiss" type="button">x</button>

As far as one knows, the value attribute on <button>s are not supported by IE7, it pulls from the innerHTML (the content between the opening and closing <button> tags) inplace of reading the attribute's content.

According to me we don't need to bother about this because of the two reasons: IE7 usage is way down, and it seems rather uncommon to set both a value and the innerHTML on <button>s.