According to some interpretations of the Bible, Hell isn't actually a real place. The bible typically refers to Hell as an 'everlasting fire,' which could be a metaphor for destruction and oblivion. The logic being, since God is the source of all life in existence, turning away from God leads only to annihilation. Modern conceptions of Hell as a physical place with lava and demons and poetic justice torture scenarios for sinners originate mostly from Dante's Divine Comedy rather from any established religions canon.
But I digress. Personally, I seem to agree more with zidine100's idea that after a certain period of time people would probably start to get desensitized to typical torture scenarios. My belief is that, over time, souls that are imprisoned in Hell start to take on characteristics of Hell itself, gradually turning into demons and taking up arms against God and the righteous alongside his army of demonic hordes. Most of them probably won't amount to anything more than cannon fodder during the final battle of apocalypse though; eviscerated guts clogging up the proverbial tank tracks.
To be honest, I've always wondered how one reconciles the concept of Hell as a place of eternal suffering and torment with the concept of a loving and all-powerful God. It seems that God would probably just *****-slap some empathy into the evil bastards (which, by most interpretations of the Bible includes just about everyone) by forcing them to go through all the suffering they caused in their past lives, and then have them apologize, make up for it somehow, call things even, and let them into Heaven; one might call this the Purgatory Method. Of course, this only makes sense if God is actually loving and forgiving and has any interest in redeeming humanity. If God is a vengeful Nazi asshole then it makes perfect sense that he would trap anybody who doesn't follow his rules and isn't a (insert Christian/Jewish/Islamic denomination here) in a place of eternal torment.
Because, you know, subjecting people to horrible physical and/or psychological agony for millions of years is a great way to make them into kind, loving, generous souls who like to kiss adorable kittens and buy presents for small children and NOT make them into insane, vengeful, bloodthirsty monsters without a shred of humanity left in them. Right?