I think it's probable that Cash thought the song spoke to him, so I too think it's personal (like Reznor's original version obviously is as well).
The Devil Went Down to Georgia by Charlie Daniels Band is a great song. It's about a boy named Johnny who has a fiddle-playing duel against the devil. He bets his soul against a fiddle made of gold (rhyme, see). The original is from 1979.
[youtube]cDm_ZHyYTrg[/youtube]
Primus made a rather awful cover which was memorable for it's claymation video and little else, at least in my opinion.
[youtube]3FRtkek-Et4[/youtube]
Wacky and zany punk-band Toy Dolls actually did a better job when they made a punked up version that replaced Georgia with Scun
thorpe (title: The Devil Went Down to Scun
thorpe) and changed the fiddle for a guitar. Here it is - although whoever upped it shamelessly stole the vid from the Primus version, effectively corabining the best features of both covers

:
[youtube]ujcaq5K_cjk[/youtube]