I have used ProPhoto RGB as my working space almost as long as I have been using raw format -- for the first couple of months with my D30 I shot JPG and then discovered the Joy of Raw. I started working with WideGamut RGB using the LinearSharpen Action originally developed by Pekka Saarinen.

There's been loads of bandwidth burned on forums and web sites about whether it's a good idea to use ProPhoto RGB or not, I've tried to pull the main themes together in this mind map.