[Ibrîniðilpathânezel]

The case of Frodo, Bilbo, and even Gollum is not the same as the Elves, as they were all Mortals and the Elves were not. Frodo was specifically told that a Mortal who wears a Ring of Power is not affected by it in the same way. I rather suspect that, aside from Hobbit toughness, the reason Gollum did not turn into a Ringwraith was because he had the master ring, not one that had been specifically designed to turn its wearer into a thrall, as in the case of the nine and the seven (and we know that the seven didn't work because of the nature of the Dwarves). It is also said that when Sauron put on the One, the owners of the Three took off their rings, knowing they had been betrayed. To me, the implication here is that unless Sauron has the One in his possession, it's safe for the keepers of the Three to wear and use their Rings. Given the purposes for which they were made (and especially the fact that of the Three Keepers during the time of LotR, only Gandalf was an extensive traveler), I can't see that any purpose would be served by putting it on and taking it off all the time; indeed, for Lothlorien and Rivendell, it would seem wiser if those who were using the rings to help protect their lands kept them on as much as possible.

To me, the incident at Galadriel's mirror, in which Frodo sees her ring and Sam doesn't, is a very clear statement that the rings can remain hidden while on the owner's hand, unless the owner wishes otherwise, or the person looking has a greater ring in their possession. When Tolkien said that Gandalf wore Narya "openly," I don't believe he was implying that Gandalf had taken it out of his secret pocket or off the chain around his neck; he had merely stopped exerting his will to keep it from being seen by the eyes of others.

Now, if this method of concealment was effective with Saruman, I suspect it would have given Saruman even greater reason to hate Gandalf and think that he was trying to usurp his position. But that's another kettle of fish.