O how great the goodness of our God, who prepareth a way for our escape from the grasp of this awful monster; yea, that monster, death and hell, which I call the death of the body, and also the death of the spirit.
And because of the way of deliverance of our God, the Holy One of Israel, this death, of which I have spoken, which is the temporal, shall deliver up its dead; which death is the grave.
And this death of which I have spoken, which is the spiritual death, shall deliver up its dead; which spiritual death is hell; wherefore, death and hell must deliver up their dead, and hell must deliver up its captive spirits, and the grave must deliver up its captive bodies, and the bodies and the spirits of men will be restored one to the other; and it is by the power of the resurrection of the Holy One of Israel.  2 Nephi 9:10-12

...wherefore, they who are filthy are the devil and his angels; and they shall go away into everlasting fire, prepared for them; and their torment is as a lake of fire and brimstone, whose flame ascendeth up forever and ever and has no end. 2 Nephi 9:16

O the greatness of the mercy of our God, the Holy One of Israel! For he delivereth his saints from that awful monster the devil, and death, and hell, and that lake of fire and brimstone, which is endless torment. 2 Nephi 9:19

For the atonement satisfieth the demands of his justice upon all those who have not the law given to them, that they are delivered from that awful monster, death and hell, and the devil, and the lake of fire and brimstone, which is endless torment; and they are restored to that God who gave them breath, which is the Holy One of Israel. 2 Nephi 9:26

It's pretty clear from the Book of Mormon that Joseph Smith believed in a literal hell, where people, the devil and his angels live in torment, that is defined as a spiritual death or separation from God.  He calls it an "endless" torment, meaning "forever" and "without end."

However, Mormons believe hell is temporary...for most people. 

HELL: Latter-day revelation speaks of hell in at least two senses. First, it is the temporary abode in the spirit world for those who were disobedient in mortality. In this sense, hell has an end. The spirits there will be taught the gospel, and sometime following their repentance they will be resurrected to a degree of glory of which they are worthy. Those who will not repent, but are nevertheless not sons of perdition, will remain in hell throughout the Millennium. After these thousand years of torment, they will be resurrected to a telestial glory (D&C 76:81–86; 88:100–101).

Second, it is the permanent location of those who are not redeemed by the atonement of Jesus Christ. In this sense, hell is permanent. It is for those who are found “filthy still” (D&C 88:35, 102). This is the place where Satan, his angels, and the sons of perdition—those who have denied the Son after the Father has revealed him—will dwell eternally (D&C 76:43–46). 

(From the LDS website: http://www.lds.org/scriptures/gs/hell?lang=eng&letter=h)

This entry straight from the LDS website says:

• People have an opportunity to accept the gospel, repent and leave hell.
• Those who refuse will remain in hell for a thousand years, then they will go to telestial glory, which is kind of the ground floor of heaven. 
• Finally, the "filthy" (Satan, demons and sons of perdition), those who deny Christ will live in hell.

There are some fundamental problems with that view of hell.

• Jesus never speaks of a second chance after we die.  If there was, wouldn't he mention it?  How could anyone know this valuable information but Jesus Christ?
• The Bible is clear that everyone dies once and then faces judgment.  Just as people are destined to die once, and after that to face judgment...Hebrews 9:27
• Purgatory is never found in the Bible.  See: http://www.reasonhope.com/2011/10/is-it-true-that-there-is-place-before.html
• There is no distinction of sinners in the Bible.  "Perdition" means hell.  A son of perdition is one who makes his home in hell.  There are two degrees of sinners in the Book of Mormon - those who reject God and those who REALLY reject God.  What's the difference?
• What makes the Book of Mormon believe that people will accept on the other side?  If people can accept on the other side, why accept here on earth, if we have another chance?  I could murder on earth without repentance and still get into heaven, eventually.
• The Book of Mormon more closely describes a Biblical hell than the future revelation of hell given in Doctrines and Covenants written by Joseph Smith in 1832.  DID JOSEPH SMITH RECEIVE CLEARER INFORMATION ABOUT HELL THAN JESUS?

The Mormon church has a narrow view of how many will be in hell.  It sees hell emptying out with people accepting Mormon doctrine.  Jesus in Matthew 7:13-14 says the road to destruction (Hell) is wide and many will go to it.

2 Nephi 28:21-23 says many churches (Joseph Smith believed that included all of them) that preach a false doctrine (not Mormonism) were going to hell.  That's a lot of people!

So is hell heavily populated or sparsely populated?  Is hell "endless" or "temporary"?  Even Mormons seem confused as to what hell is.