Asking for practical advice on choosing /48 vs. /56 on a residential broadband CPE is largely unanswerable. Because I don't know of any residential broadband CPEs that support IPv6.
If you go to http://www.getipv6.info/index.php/IPv6_Presentations_and_Documents there is at least one presentation from Comcast, a residential broadband provider who explained that they simply cannot continue in business without IPv6. They started IPv6 deployment planning in 2005. If you don't know of CPE that supports IPv6, maybe you should ask a broadband ISP that is serious about surviving in business past the crunch of 2010.
I want to be wrong about that. Seriously. Send me a link to one. I want to be wrong. (And by residential, I mean a CPE/router/firewall that costs less than $150US.)
http://wiki.openwrt.org/IPv6_howto Clearly, this CPE is based on Linux which has had full IPv6 support for many years, including things like firewalling, transition mechanisms like 6to4, DNS and so on. Given the realities of today's low-end network device manufacturing (centered in China where IPv6 is already being deployed, and based on standard hardware designs that are differentiated by software, plastic case design, and packaging) it should take about two months from time of order for mass quantities of CPE devices to appear on the market. The software is already done, the standard hardware designs are fully capable of IPv6. All they are waiting for is customers like Linksys to place an order.
IMO, the only answers so far: businesses get /48 dialup gets /64
Wrong! The answer so far is that EVERYBODY gets a /48, but if you think that there is a risk that you won't be able to get additional /32s when you outgrow your first allocation, then give a /56 to RESIDENTIAL SITES. This is not the same as dialup, i.e. residential sites could be connected with DSL, T1s, wireless, or whatever. In fact, if a business is connected via dialup, you should give them a /48, because businesses have a habit of continuous growth, unlike residences which tend to top out at 5 or 6 residents. --Michael Dillon