I bought the PDF (mostly for the Excel sheet) a while back and have been lovin' it ever since. I use it for pretty much all of my d20 games (D&D, Modern, GT). Determining ELs, XP, etc. It also lets me plan encounters ahead ... how much XP do I want to give out? How hard an encounter do I want? How should I build the foes to match that? I did that for last Sunday's game, where I knew I wanted a long, challenging, but ultimately non-deadly combat with a "Plant Monster" that turned out to be an undead fey (defeated the plant, the fey emerges from it, battle the fey). I was able to plan out my CRs ahead of time and then use the creature creation spreadsheet to build the perfect threat for the CRs I needed.
Shweet.
--fje