Most of the time I have seen it deployed it was enabled for just a couple of select pages (homepage etc). I think the sweet spot for it follows the 80/20 rule: do the 20% of pages that absorb 80% of the traffic.
Principal Consultant International Business
Member of the Community Project Board
If you have a site with no user specific data shown you can deploy static cache and get nice speed boost. But keep it for homepage and main categories, do not use if for all content.
If you have user specific data then you could still use static cache but then you need to implement some AJAX calls for those user specific elements...