I think the reason that cache invalidation scheme is not in wider use is that it's not very generalizable, and as data model complexity increases things get out of control. If someone adds a new post, you may end up having to regenerate the post page, the pages before it and after it, an authors page, any number of tags pages, etc. So I think it works sometimes in specific instances, but not as a general caching strategy.

If it worked though, it would seem to be the most beneficial. Is anybody working on it?