This site died sometime after February 2012.
- This site stopped supporting World of Warcraft users around February 2012.
YouPVP.com is a website that collects (via a custom client) PVP statistics, and then aggregates them to provide analysis on win/loss percentages, opponent win percentages, and other higher level statistics.
The client installer appears to run on Windows XP or better only, but uses an AddOn to collect data. No obvious information about uploading data for non-Windows users.