Like other good bearing materials, silver is soft and won't score the mating journal surface. Another property of bearings is that large contaminants should embed themselves into the soft metal to reduce scoring of the journal surface. Silver excels in these characteristics. Gold is better.
Galling - or resistance to galling - is another important property of a bearing material. Lead, tin, silver, and gold are excellent in this respect.... aluminum is horrible.
Aerospace uses bronze bearing cages that are coated in silver because of silver's superior performance in "rubbing" applications. I've also heard stories that silver was used in journal bearings way back when for some high-end vehicles (Cadillac?).
