GRI G4 (Global Reporting Initiative) as a waste min "playbook"?

For those who are using GRI/G3/G4 reporting, share with the class a little bit about what you've seen:

• Is it really as intimidating as it looks?
• Did you go "all in" or did you begin with selected subparts and start reporting there?
• How long did it take for your first report? If you've reported more than once, any easier the second time around?
• Where G3 was a bit more condensed, G4 appears to be significantly farther ranging... is G4 worth the extra effort?

For those unfamiliar with GRI reporting:
http://en.wikipedia.org/wiki/Global_Reporting_Initiative