IPv6 reverse zones advise

[a.smith at ukgrid.net]

Hi,

   we will shortly start using IPv6 reverse DNS, and having never used  
it before I thought Id ask those with some experience if they have any  
words of wisdom before I make any horrible mistakes ;) Ive already had  
a good read of a good many sites on the subject but still would like  
to check a couple of things.
When creating IPv6 reverse zones can the subnet be as large or small  
as you like? Ive seen examples using /48 and /64, can this be  
effectively whatever you want?
And following on from that if it is user definable, what would be the  
recommended way (size) forward? We are using flat file zone files. To  
me the simplest would seem to create the zones using large subnets and  
where necessary (as occasionally we are asked to do) delegate via the  
zone file some ranges to other DNS servers.
Im not an expert in all of this really, but we get by on IPv4 so if  
anyone has any tips they would be greatfully recieved,

thanks Andy.