Salvation & the Holy Ghost

Holy Ghost
Mormons believe that once you recieve the Holy Ghost, the Holy Ghost comes and goes depending on if you are living righteously or not. In other words, if you stop living righteously the Holy Ghost leaves you. If you start living righteously again the Holy Ghost comes back to you.

Christians believe that once you recieve the Holy Ghost, the Holy Ghost stays with you, continually renewing you and sanctifying you.

Salvation
To a Christian salvation means that you are saved by grace through faith in Christ. You have forgiveness of sins, are made righteous in Jesus and will be with God in Heaven.
You are reborn!!! Christ paid it all on the cross!!!! Praise God!

Mormon View:
Have you ever heard: Mormons think every one is saved?
Ever also heard: Mormons think that only they are saved?
Which one is true? --Both are true. Confusing huh? 
This is because there are two different meanings of "salvation" to mormons. Here are the two meanings:

1. Saved from physical death in the resurrection. Everyone will be resurrected. Everyone gets salvation here and then will go on to one of the "degrees of glory" (heaven) or "outer darkness" (hell)

2. Being cleansed from sin and being with God in the celestial kingdom (highest degree of glory). Only a faithful mormon can get to the celestial kingdom.

So, not everyone who does not attain salvation will go to "outer darkness" (hell). Some who dont attain salvation will go to one of the two lesser kingdoms of glory (terrestrial kingdom or telestial kingdom) and very few will go to "outer darkness" (hell) as this is for the "really really bad" people. They call these "really really bad people" the "sons of perdition".