Carbon balls are less prone to magnetise but they too can eventually cause sticking and trough problems.
Like I said, my ACDC and Avengers have Blink balls and I have not (yet) experienced magnetized issues. The playfield is certainly cleaner where the rag would come up grey after a wipe following a number of plays with standard carbon balls.
The following article is very good and useful for anyone with balls of steel.
http://www.pinballnews.com/learn/magnetism/index.html
