The SmugMug feature page lists one of the features available across all accounts as "Unlimited photo uploads" and "Unlimited traffic".
I hear terms used like this today and am weary of what that actually means. For example, unlimited data usage on many cellphone plans that are listed as unlimited, are in the fine print- not actually unlimited.
Do serious professionals with very high traffic rates and or a very vast collection exist? If so do they have to pay more? This is all meant to focus on a single question(as stated in the title, I am simply suggesting supporting topics that would enforce that answer).