If my memory serves me correctly (< /Iron Chef! >) book-Gandalf did touch the Ring at least once, I think he picked up the Ring after Bilbo dropped it, put it in the envelope, sealed the envelope, and then put it on the mantle. But I think that's the only time Gandalf touched the Ring in the book. I'm pretty sure I'm right, 'cause after my first viewing of the movie I went back to the book to check on that... I actually preferred the movie version where Gandalf refused to touch the Ring.
Yeah, that's what I'm referring to. So it seems like touching the ring briefly (as opposed to actually USING the ring) wouldn't necessarily ensnare someone, but using it would be extremely dangerous.