If you have downstream customers, even if they're just dialups, expect to assign at least a /60 to each one. Many folks recommend /56 or /48.
ARIN counts a /56 or a /48 per customer, your choice. There is no point in allocating less. More to the point, soon the IPv4 address shortage and the transition to IPv6 will hit the mainstream press, and hundred of writers will be writing advice columns about it. From their point of view, more for the customer at the same price is better, and I fully expect that they will be advising folks to make their ISP choice based on how much address space is allocated. If you allocate less than a /56 per customer, then you won't be able to sell to new customers or hang on to old ones. Just don't do it, because you are only damaging your own business. ARIN will not give you a discount or give you better terms just because you allocate a /60 to dialup customers. There is simply no benefit to you or to the networking community in allocating a prefix longer than /56. --Michael Dillon