"May Elbereth protect you."

[Arvedui]

This paragraph from the conversation between Gildor and Frodo triggered a chain of thought:

'I am deeply grateful,' said Frodo; 'but I wish you would tell me plainly what the Black Riders are. If I take your advice I may not see Gandalf for a long while, and I ought to know what is the danger that pursues me.'
'Is it not enough to know that they are servant of the Enemy?' answered Gildor. 'Flee them! Speak no words to them! They are deadly. Ask no more of me! But my heart forbodes that, ere all is ended, you, Frodo son of Drogo, will know more of these fell things than Gildor Inglorion. May Elbereth protect you!

Could it have been that this "prayer" was indeed recognized by the Powers?
We have of course the happening at Weathertop:

At that moment Frodo threw himself forward on the ground, and he heard himself crying aloud: "O Elbereth! Gilthoniel!" At the same time he struck at the feet of hsi enemy. A shrill cry rang out in the night; and he felt a pain like a dart of poisoned ice pierce his left shoulder.

And Strider's comments after the fight:

'Look!' he cried; and stooping he lifted from the ground a black cloak that had lain there hidden by the darkness. A foot above the lower hem there was a slash. 'This was the stroke of Frodo's sword,' he said. 'The only hurt that it did to his enemy, I fear; for it is unharmed, but all blades perish that pierce that dreadful King. More deadly to him was the name of Elbereth.'

 

[Starflower]

I think it is very possible that the Valar did heed Gildor's blessing. Tolkien implies in several places that the Valar kept a lookout so to say on M-E, even after the sundering. Maybe the Queen of the Stars recognized the importance of what Frodo was set out to do and did indeed extend her 'protection' over him. After all, Galadriel gives Frodo the star-light in Lorien and the name of Elbereth was the very thing to evoke the light to shine from within the glass

 

[Eriol]

We must not forget Tolkien's words about Elbereth and Manwë's perception when they are sitting together upon Taniquetil. We must not forget, but I don't have them here, and won't paraphrase, so if someone would oblige...



I think it is very clear, from that passage, that Elbereth hears prayers of that sort. Less clear is whether she acts upon them or not; but still, the Valar retain the ability to walk unclad, and Frodo's quest was certainly on their radar screen . She may have helped, in some gentle way.

 

[Ithrynluin]

I'd say the Valar did intervene at some crucial points, much like the eagles (or it could be said that Manwë, for example, intervened through the eagles), but I think these occurences were very rare, since they withdrew themselves from Middle-earth and did not involve themselves directly; the Istari, too, were forbidden to engage Sauron directly.

Here's the passage Eriol mentions:

The Silmarillion; The Valaquenta
Manwë and Varda are seldom parted, and they remain in Valinor. Their halls are above the everlasting snow, upon Oiolossë, the uttermost tower of Taniquetil, tallest of all the mountains upon Earth. When Manwë there ascends his throne and looks forth, if Varda is beside him, he sees further than all other eyes, through mist, and through darkness, and over the leagues of the sea. And if Manwë is with her, Varda hears more clearly than all other ears the sound of voices that cry from east to west, from the hills and the valleys, and from the dark places that Melkor has made upon Earth. Of all the Great Ones who dwell in this world the Elves hold Varda most in reverence and love. Elbereth they name her, and they call upon her name out of the shadows of Middle-earth, and uplift it in song at the rising of the stars.