I looked up what the thundering herd problem is but still don't really understand how it applies here? Could you explain further? (Sorry if thats a dumb question, not a computer scientist here).
Hmm. If this project ever expands to a larger audience than the one intended here, I will definitely look that up. Until this happens, I'll apply the YAGNI principle. :)
Have you considered using varnish + cassandra? Take care to avoid the thundering herd problem.