Once in a while, you'll come across some lead or tin capsules on an old bottle. These capsules are weighty, you have to press harder with the corkscrew blade to cut into it, and the capsules are sharp and unforgiving if you cut yourself while opening the bottle.
Here is a great article on the rising cost of tin capsules. Not only has the price of tin increased, but the weakened American dollar has made it difficult for US wineries to purchase European tin capsules (the price rising 250% in the two year period of 2006-2008), and the weak dollar has tempted export markets in regions such as South America and New Zealand look to US-made screw caps and synthetic capsules for bargains.