Re: Brown Tongue
It's called Black Hairy Tongue (gross name but seriously that's the medical term for it). It's a condition that happens when the papilliae on your tongue (the tiny little bumps that give your tongue it's texture) become elongated. These papilliae, just like your skin, shed themselves off regularly and replace themselves with new ones. They become elongated and big when this natural shedding of dead tissue fails to occur. The brown colour you see on your tongue is bacteria and other gunk getting trapped between the elongated papilliae. That's why you can scrape or brush it off. Give your tongue a good brushing with your toothbrush, then have a look at it. You'll see the elongated papilliae - your tongue will look fuzzy or hairy.
This condition can be caused by many things. The over-use of mouthwash can kill off certain bacteria that are supposed to live in your mouth and control the natural shedding of tissue. There are also some wide-spectrum antibiotics that need to be used to fight certain ailments, but they are so strong that they also kill off the "good" bacteria that is supposed to be in your mouth. Heavy drinkers and smokers also can cause the same problem - the booze and/or smoke kills off the bacteria. It sounds yucky, but there are types of bacteria in your mouth that "eat" away the dead papilliae off your tongue. If you kill them, you get the Hairy Tongue.
You can get rid of it by stopping whatever you're doing to kill the bacteria, and by routinely brushing and scraping your tongue.