All that being said, to help you out, here are some examples of when to use commas, and when not to use commas:
"The girl ate some food, because she was hungry."
"He saw the guy, whom he talked with yesterday."
"The file, that I started downloading, has finished."
Those are all wrong. They sound like somebody from Germany failing at English. These ones are right:
"The girl ate some food because she was hungry."
"He saw the guy whom he talked with yesterday."
"The file that I started downloading has finished."
tl;dr: Simply never use commas ever!
In seriousness, nice thread. I never know when to place commas in my sentences, so I am likely one of those offenders. Sorry! It wasn't personal, I assure you.
Also - be honest - did you read your post through several times to be 100% super-sure you didn't make any comma-mistakes?
SUPER-EDIT: I actually had "Please send me a PM and let me know when I made a language mistake!" in my signature for the longest time. I got exactly one PM correcting my language.
