To my understanding Reddit serves a highly customized content to each logged in user. Can you help me understand how HTTP level caching will solve this problem more efficiently than their service level caching does right now?
Logged out users see a "snapshot" of the page updated every so often.
And I really don't think that caching pages per session would really help with their load all that much. Why not just use HTTP cache headers at that point?
Plus while you don't really need to show votes ASAP, logged in users will want up to date comments.