I personally believe the companion part of the game could be much more important then FO3's,
storywise they could completely change moral choices for the game, for example,
you've joined up with this Girl and maybe developed an attachment to her.
You have been wondering around the Mohave wasteland for too long and have run out of water,
your Girl companion has fainted from the heat and needs water before she dies, a wasteland dweller comes across you,
you ask for some water but he only has enough for himself to get to New Vegas, you have Three options:
Good option: let him pass and give her your water and see if you can last the journey.
Bad option 1: You can kill him and take his water so both you and your girl can continue together.
(both above options can gain her love for saving her.)
Bad option 2: You kill him, take his water but abandon her to the wastes (super bad karma boost, also maybe she some how survives and comes back for revenge.)

Please join one of the open threads on the subject instead of starting a new one.

See http://www.gamesas.com/index.php?/topic/1094816-what-do-you-want-in-new-vegas/
or http://www.gamesas.com/index.php?/topic/1096854-hardcoe-mode-companions/
or http://www.gamesas.com/index.php?/topic/1095781-invent-you-own-companion/