Apologies if it looks like I'm purely talking to LT. Oh heck... I am ...sorry!
LT - Loaded question - does God make mistakes?
A mistake suggests that there was a better way to do something. I think that's a whole different thread that would potentially be a christians v aethiests thread :)
Does receiving the Holy Spirit entail being saved? Well I do think I've quoted reams of scriptures that say that we have to do something about our faith (theres a scripture which talks about baptism being required for being saved.) So assuming that your question means: ignoring all the quoted scriptures so far, does having the Holy Ghost mean you are saved?
Let's have a look.
Acts 5:32
32 And we are his witnesses of these things; and so is also the Holy Ghost, whom God hath given to them that obey him.
Acts 19:2 - 6
2 He said unto them, Have ye received the Holy Ghost since ye believed? And they said unto him, We have not so much as heard whether there be any Holy Ghost.
3 And he said unto them, Unto what then were ye baptized? And they said, Unto John's baptism.
4 Then said Paul, John verily baptized with the baptism of repentance, saying unto the people, that they should believe on him which should come after him, that is, on Christ Jesus.
5 When they heard this, they were baptized in the name of the Lord Jesus.
6 And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied.
Matthew 28:19 - 20
19 ¶ Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
20 Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen.
John 3:5
5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
looks like one interpretation of this scripture is a need for water and the spirit. It does seem to go hand in hand - baptism by water and then baptism of Holy Ghost.
I've done some searches looking for scriptures which include the word saved and ghost / spirit and I got this one:
Titus 3:5
5 Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost; Which backs up what I said (works don't save us) but mentions baptism (washing of regeneration?) and the Holy Ghost making us born again (renewing?) is required for the saving power to be made manifest.
I'll quote LDS doctrine here just to be indulgent:
Articles of Faith 1:3 - 4
3 We believe that through the Atonement of Christ, all mankind may be saved, by obedience to the laws and ordinances of the Gospel.
4 We believe that the first principles and ordinances of the Gospel are: first, Faith in the Lord Jesus Christ; second, Repentance; third, Baptism by immersion for the remission of sins; fourth, Laying on of hands for the gift of the Holy Ghost.
I guess our point of disagreement is on the 3rd and 4th ordinaces - baptism and Holy Ghost by laying on of hands. I presume we are both in agreement on 1 and 2.