I noticed (thanks to Products.LongRequestLogger) that on pages where lots of comments are shown the requests have two really big keys: _oai_cache and _plone_ec_cache.
They both are related to caching workflow related data (on those pages with lots of comments, below each comment there is a list of all possible workflow actions for the given user).
So for each comment (or any call to workflow_tool.listActionInfos) a new entry is added to both caches.
Should I be worried about it? Or not at all?