[Gordis]

Originally Posted by Fordim Hedgethistle

Which brings me back to Frodo...who seemed so entirely selfless throughout that even the Ring couldn't find anything to 'use' against him(?) Making him the only TRULY selfless person in the tale??

Frodo was indeed a good hobbit and a selfless person by nature. At the beginning I have no doubt that saving the Shire (and the rest of ME) was his greatest desire. But during the long journey the Ring and Sauron's superior will in it were rubbing on him, slowly poisoning is mind, making him forget the Shire and his priorities:

No taste of food, no feel of water, no sound of wind, no memory of tree or grass or flower, no image of moon or star are left to me. I am naked in the dark. Sam, and there is no veil between me and the wheel of fire. I begin to see it even with my waking eyes, and all else fades.

By the end of the Quest Frodo becomes quite un-hobbity in mind, sort of wannabe Dark Lord-ish. We have glimpses of the process. Look how Frodo intimidated Gollum:

For a moment it appeared to Sam that his master had grown and Gollum had shrunk: a tall stern shadow, a mighty lord who hid his brightness in grey cloud, and at his feet a little whining dog. [...]
Then suddenly, as before under the eaves of the Emyn Muil, Sam saw these two rivals with other vision. A crouching shape, scarcely more than the shadow of a living thing, a creature now wholly ruined and defeated, yet filled with a hideous lust and rage; and before it stood stern, untouchable now by pity, a figure robed in white, but at its breast it held a wheel of fire. Out of the fire there spoke a commanding voice.
‘Begone, and trouble me no more! If you touch me ever again, you shall be cast yourself into the Fire of Doom.’

No really, is it a hobbit speaking?

Look also what happened in the Morgul Vale:

He knew that the Ring would only betray him, and that he had not, even if he put it on, the power to face the Morgul-king – not yet.

Intresting this "not yet". I take it he was diluding himself with the idea to claim the Ring in order to be able to face off the Nazgul... The idea was already there and it would only grow.

And finally in the Cracks of Doom

Frodo stirred and spoke with a clear voice, indeed with a voice clearer and more powerful than Sam had ever heard him use, and it rose above the throb and turmoil of Mount Doom, ringing in the roof and walls.
‘I have come,’ he said. ‘But I do not choose now to do what I came to do. I will not do this deed. The Ring is mine!’ And suddenly, as he set it on his finger, he vanished from Sam’s sight.

I don't think Frodo was thinking of saving the Shire at the moment. Not anymore. In his deluded mind, poisoned by the Ring, he contemplated becoming the Ringlord, ruling ME, ordering about the nazgul. He was not Frodo anymore, he was a strange mixture of Frodo and Sauron from the Ring, with the latter clearly prevailing. The Ring acted not so much on Frodo's own desires, but on Sauron's desires implanted in him. That's why he felt so empty and broken with the Ring destroyed and could never enjoy the Shire again.