Single output file per reduce key?

Hello,

I'd like me reduce tasks to each output a single file per key,  
containing the value. Each file would be named with the key.  It  
appears that I need to (at least) create a new OutputFormat and  
possible a RecordWriter.  As doing this would likely involve a lot of  
trial and error on my part, I was curious if someone had implemented  
this already and would like to share.  I will be needing both versions  
that write text files and binary files eventually.

Short a full existing implementation that I can steal, how about some  
hints?

Cheers,
Myles