Synsepalum dulcificum

Imagine drinking Tabasco sauce and thinking it tasted like a sugary glaze, or drinking a bitter beer that your taste buds are certain is chocolate. Imagine having a magic pill that could turn lemons into candy. Well, you don’t have to imagine. Like a magical treat straight out of Willy Wonka’s candy factory, the berry known as “miracle fruit” has the odd ability to rewire the way the tongue perceives bitter and sour flavors for up to two hours after consumption. The fruit has been growing in popularity in the US as the guest of honor at bizarre soirees known as "flavor tripping parties" where tasters eat the strange little fruit and then consume sour and bitter foods to experience the oddity of how their tongue transforms the flavors in a reality-defying fashion.

Read on:
http://www.dailygalaxy.com/my_weblog/2008/06/miracle-fruit-1.html
http://en.wikipedia.org/wiki/Miracle_fruit
http://www.offiziere.ch/?cat=24
http://www.miraclefruitman.com/

.. after eating [miracle fruit] stout beers taste like chocolate milkshakes, grapefruits taste like pixie sticks, cheeses taste like frosting, it will make even the crappiest tequila taste like lemonade (and strangely enough, it will make all wine taste like Manischewitz).
- Flavor Tripping blog, entry "mad flavor science"