2^128 is a "very big number." However, from a network engineering perspective, IPv6 is really only 64bits of network address space. 2^64 is still a "very big number."
An end-user assignment /48 is really only 2^16 networks. That's not very big once you start planning a human-friendly repeatable number plan.
An end-user MINIMUM assignment (assignment for a single "site") is a /48. (with the possible exception of /56s for residential customers that don't ask for a /48). I have worked in lots of different enterprises and have yet to see one that had more than 65,536 networks in a single site. I'm not saying they don't exist, but, I will say that they are extremely rare. Multiple sites are a different issue. There are still enough /48s to issue one per site.
An ISP allocation is /32, which is only 2^16 /48s. Again, not that big.
That's just the starting minimum. Many ISPs have already gotten much larger IPv6 allocations.
Once you start planning a practical address plan, IPv6 isn't as big as everybody keeps saying...
It's more than big enough for any deployment I've seen so far with plenty of room to spare. Owen