Memcached is a wonderful tool, but a standard integration with Rails will raise the issue of performing caching based on the uri of the request, hence, if you activate caching for an action that handles POST requests you will be in trouble: users will receive a result cached for someone else until the expiration. 

I did not like the idea of switching to a GET request: it's widely used, but it can get ugly. My approach is to serialize the values of the form into a md5'ed string and append it to the form action url.