My dad relies heavily on email for his work, he will exchange several documents a day and in about 5 years we still haven't reached 1GB
I think the 1GB thing is pretty superficial... i reckon what they're really thinking is "the average account will reach X megabytes and we're prepared to give way over that". 1GB is just a way of saying they'll give you whatever you need... so they probably won't set aside 1gb for every account they have.