Could someone explain about Feanor and "doing time" I'm somewhat at a loss.

In short, Tolkien believed that Elves were to be immortal, but because of Melkor's corruption of Middle-earth they could die. When they died, Elven spirits were to go to The Halls of Mandos where they were to purge themselves of any evil that their corrupted bodies added to their souls in life. It is very similar to the Catholic concept of purgatory.

Once the evil has been purged, the Valar were to create new bodies for the Elven souls to enter so that they may live once again.

Feanor was so screwed up and hateful that I don't think he was ever able to purge the evil from his soul.

No, I think Feanor saw the error of his ways. He is not to be reincarnated until the Dagor Dagorlath. That's his punishment, it doesn't mean he is still hateful and screwed up.

Feanor's hate was very strong. Do you have any textual support for the idea that Feanor's time in Mandos was punitive in nature?

Thanks for clearing that up for me.

I'd rather say purgative, but this is a subtle distinction. It can also be considered as punitive [img]smilies/wink.gif[/img]

(Bold is mine).

This is exactly why I don't believe Feanor could ever be rehoused. He still harboured malice against others.