I just sold my first PaperCut installation. While I haven't been involved in a physical installation yet, I've seen PaperCut's WebEx presentation several times and I've yet to see any real differences in PaperCut vs. Print Audit (other than price). I'm not saying they don't exist, just saying I was fairly impressed with the features touted in the presentation (and obviously, so was the client that purchased the software).
JasonR's comments regarding PaperCut's inability to track copy/fax/scan usage is true of PaperCut NG product that can be purchased directly by anyone via the internet. However, PaperCut MF is a dealer-only product that works with most major MFP manufacturers to track all usage on stand-alone printers and MFPs as well.
In the sale I just made, PaperCut was the one deciding factor for the client that made the sale a "no-brainer". Their new-found ability to charge-back clients for pages printed at desktop printers actually reduced their monthly expenses after the installation of all new equipment.
Needless to say, at this point I'm a huge fan of the solution. I'll keep you posted as I begin the implementation.