Every now and then, what seems like a golden opportunity comes up: you start the game with five coppers, and the Mint is in play. By purchasing this, you can instantly trash five of your starting copper. However, this leaves you with only two copper in your deck: not enough to purchase a silver.
Say your second buy is the third copper you need for the silver. Now there are seven cards in your deck: three copper, three estates, and a mint. This means there is about a (correct me if my math is off) 30% chance that you'll only draw two coppers on your third draw.
If some 2 cost cards are in play, this is less of a problem. Having a Moat or Cellar, for instance, could draw out coppers, and Secret Chamber or Lighthouse could provide the necessary money to obtain the first silver.
This has already been discussed a bit on Dominion Strategy, but there doesn't seem to be much of a consensus.
When, if ever, is buying a Mint for your first or second buy an optimal move?