"Russian-Doll Caching" is great. It embraces the Rails (and Ruby) goal to "make the developer happy". And it does. Not having to worry about cache expiration is superb.
It has its limits, though. If you're trying to avoid any database queries, russian-doll caching will not work for you. If you are trying to represent thousands, or even hundreds, of objects under a single cache fragment, russian-doll caching is not the best option.
We use it whenever it makes sense, but sometimes we just have to bite the bullet and expire a cache fragment manually. When you want to start manually expiring cache on a fairly busy website, you have to start considering race conditions. I recently ran into the following scenario:
class Post < ActiveRecord::Base
after_save :expire_cache
