Eric Lawrence, creator of Fiddler, put together an excellent post about issues with setting the max-age Cache-Control setting for too far in the future.

Remember, setting max-age correctly in the Cache-Control header can improve web performance by instructing a client’s browser to keep the object in cache and refer to it for future requests.  This will keep a user from re-downloading the object.

Check out the post here: http://blogs.msdn.com/ieinternals/archive/2010/01/26/Use-Max-Age-values-less-than-MaxInt.aspx