This is a common trick used by flight attendants across the country. I picked up the tip while working for a major US carrier and have used it every since. It is true that many spoon handles will not fit into a bottle, but you can normally find at least one such utensil that will work. I have never had it fail me, keeping the bubbles going for up to a week. 
At Christmas 2011, I tried this one with a blind test. Everyone could tell the freshly-opened bottle from the two bottles opened the night before, but the ‘silver spoon’ test was marginal: the balance of votes was for SLIGHTLY more fizz (2:1 in favour on the blind test) with the spoon.
My own suspicion is that more depends on individual bottles, storage and opening conditions than on whether there’s a spoon or not.
The origin of this research was a test some 25-30 years ago to see if champagne corks fly further at high altitudes (bigger pressure differential, thinner air). My general conclusion (sporadically checked since) is that other variables (individual bottles, cork tightness, transport of bottle) swamp altitude variables.
I have the honour,
Sir,
to remain,
Yr. Obdt. Svt.,
Roger Hicks
I could speculate that a spoon handle might somewhat obstruct the bottle opening and not provide that many nucleation sites, whereas a chain would block the opening less and substantially increase nucleation sites. Thus Cecil’s test would be invalid, without answering the question if a spoon does do anything to preserve the fizz.