Xargs to run commands in parallel

I recently found out xargs had options to parallelize what it is working on. I finally had a good reason to try it. I'm processing log files for the last year. Each day is it's own unique standalone task. My workstation is has 1 CPU with 6 cores that are hyperthreaded to give 12 logical cores. So... I asked xargs to run the processing script with 6 day log files and to run 10 processes in parallel. Zoom!
ls 2012*.tar | xargs -n 6 -P 10 process_log_files.py

Cool, I didn't know that xargs can parallelize it's work.