In line with that, if you have a /64, say, from a tunnel, is it simple to slice it up internally and hand out /96s or something?
Simple, but not recommended as it breaks autoconfiguration for that LAN, and a bunch of other potential issues. There's debate about using /112 or /126s for p-t-p connections, and /128s for loopbacks, but many still recommend sticking with /64s for those too.
If you need more subnets, request a /48. That's pretty much what ISPs will be giving end users at home (or possibly /56s depending on the ISP). Multi campus/site businesses will get multiple /48s, ISPs get /32s, etc. There's been a lot of discussion about this on NANOG and ipv6-ops lists lately.

May want to look at a this
recent post, also
RFC3177 has some guidelines about this.
The meat of the RFC here:
In particular, we recommend:
- Home network subscribers, connecting through on-demand or
always-on connections should receive a /48.
- Small and large enterprises should receive a /48.
- Very large subscribers could receive a /47 or slightly shorter
prefix, or multiple /48's.
- Mobile networks, such as vehicles or mobile phones with an
additional network interface (such as bluetooth or 802.11b)
should receive a static /64 prefix to allow the connection of
multiple devices through one subnet.
- A single PC, with no additional need to subnet, dialing-up from
a hotel room may receive its /128 IPv6 address for a PPP style
connection as part of a /64 prefix.
Note that there seems to be little benefit in not giving a /48 if
future growth is anticipated. In the following, we give the
arguments for a uniform use of /48 and then demonstrate that it is
entirely compatible with responsible stewardship of the total IPv6
address space.
-jim