If you take a look at wine bottles today, you'll note that the sealing devices are all over the place. Traditionally, cork was used, and that's still the dominant seal, but you'll also see synthetic foam-type corks, as well as screw-caps. Cork was originally used in wine because it was a relatively cheap airtight seal. It was the best available at the time. It worked pretty well, too; wines with the capacity to age will last many years if stored sideways (ensuring the cork doesn't shrink, allowing air in). However, there is a sinister side to corks.
Some corks are contaminated with chemicals called "chlorophenols." Certain bacteria and fungi can act on these to yield chloroanisoles. The chemical most often pointed to as the source of cork taint is 2,4,6-trichloroanisole:
Apparently, you can detect it down into the parts per trillion, which is similar to the thiol odorants in your natural gas. For this and other reasons, lots of manufacturers are abandoning corks. It has been suggested that the number of wines that suffer from cork taint approaches 10% (probably on the high side, though).
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The original reason for the search for a cork replacement was a shortage of cork. Wine vines only take a couple of years to produce mature grapes. Cork trees take over fifty years to produce a havestable crop. When Americans suddenly began to drink wine in the late seventies, there was not enough good cork to go around. Back in 1920, with prohibition starting in the United States, who would have imagined that one day they would need to produce enough cork for a hundred million Yankee wine drinkers. Fortunately, most of us drank crappy wine for a decade allowing the industry time to experiment with other methods of sealing bottles. It didn't take the industry long to figure out that non-cork seals were more controlable and not subject to cork taint. It took another decade to ease their way around consumer resistance.
The down side of all of this is that the cork forests are losing their value. Most traditional cork came from a type of oak bark grown in Spain and Portugal. Now that the price is dropping for cork, realestate developers are eager to get their hands on the cork forests. These same forests are a major stop for migratory birds. As Thurber pointed out: no good deed (more and better wine) goes unpunished (song bird extinction).
I remember they had a screw-cap wine on Woot Wine a while ago. There was much debate in the forums about the merits of the various closures. I'm kinda torn--I recognize the technical superiority of the screw-cap, but there's a kind of ritual in breaking out the corkscrew and popping open the bottle.
For what it's worth, I've only ever had one bottle of corked wine. Fortunately it wasn't too expensive, and I had another bottle around in reserve.