First, the "PB Copyable: Passing Complex Types" doc is *great* and the examples are excellent -- my compliments to all who contributed! My question is about the pb.Cacheable section (http://twistedmatrix.com/documents/current/core/howto/pb-copyable.html#auto9) -- specifically the first sentence: 'Sometimes the object you want to send to the remote process is big and slow. "big" means it takes a lot of data (storage, network bandwidth, processing) to represent its state. "slow" means that state doesn't change very frequently.' I would think that the product of its size and its rate of change is the applicable metric -- i.e.: the bigger the object is *or* the faster it changes (not the slower), the more applicable Cacheable is, no? Steve