Troll's clothes?

[Firefoot]

Um, rutslegolas, if Frodo's clothes weren't invisible people would see him. And clearly, people could not see him.

He simply vanished, as if he had gone slap through a hole in the floor without leaving a hole!

The Man [Boromir] gasped, stared for a moment amazed, and then ran wildly about, seeking here and there among the rocks and trees.

"Have you seen Frodo?" [asked Aragorn]
Boromir hesitated for a second. "Yes, and no," he answered slowly. "Yes: I found him some way up the hill, ... I grew angry and he left me. He vanished. ... He must have put the Ring on. I could not find him again."

If Frodo's clothes were not invisible then the Hobbits at the Prancing Pony and Boromir would have been able to "see" him, or at least know where he was at. They probably just disappeared because Frodo was wearing them.

Back to the original question...I already posted my thoughts earlier up.