Apple cider vinegar (also known as ACV for short) is properly used in salad dressings, marinades, vinaigrettes, food preservatives, chutneys and so forth. Its flavour is subtly different to that of regular vinegar in useful and interesting ways.
Unfortunately, some idiots have leapt upon it as a magical cure-all.
 Alkaline diet
Apple cider vinegar is pushed by fans of the alkaline diet who believe that these diseases are caused by the body's pH becoming too
alkaline wait, no, acidic ... Apparently, even though apple cider vinegar is acidic, it is claimed to "release" alkaline bases into the body. The mechanism is unclear.
Dangers of excessive, routine consumption of vinegar include lower bone density, lower potassium levels, possible harmful interactions with other drugs, and esophageal damage if the pill form becomes lodged in the throat.
When it is sold as a supplement in pill form, apple cider vinegar is not subject to FDA regulations, which in some cases led to boxes whose listed ingredients did not match actual ingredients or did not contain actual apple cider vinegar at all. Others listed incorrect values for the amount of acetic acid inside—which turned out to be a good thing, as the listed level would be considered toxic.
 Scientifically tested medical effects
Like many other herbal remedies, there may well be some real benefits of consuming apple cider vinegar that are only just now being explored, including possible effects on diabetes, cholesterol, cancer and, yes, the all important weight loss. But these studies are small and "suggestive" only, and no work at all has been done on appropriate amounts to consume. The wise consumer might well want to wait for more detailed studies.
 Things it's actually helpful for
Cooking, if applied properly.
If you have a sore throat, put a shot of apple cider vinegar, a spoon of honey and a shot of hot water in a cup and sip it. (You can also do this with regular vinegar if you're missing the smell of fish'n'chips badly enough.)
Distilled white vinegar can be a wonderful "green" household cleaner, insecticide and weed killer. However, apple cider vinegar in general is rather sweet because of (purposefully) incomplete conversion of the sugars in the cider into acetic acid; therefore apple cider vinegar will leave behind sugary residue and is not recommended as a cleaning agent.
Makes an absolutely delicious salad dressing.
For catching fruit flies.
If, for some hypothetical rational reason, you need to increase your intake of acids, apple cider vinegar would indeed do the trick. But honestly, unsweetened cranberry juice, or strong lemonade, would both work and taste a lot better.
- EarthClinic's article on apple cider vinegar
- 10 Health Benefits of Apple Cider Vinegar from Eat This!
- ↑ Altmedicine.about.com article on Apple Cider Vinegar
- ↑ 2.0 2.1 WebMD: Apple Cider Vinegar Page 2
- ↑ WebMD: Apple Cider Vinegar Page 3
- ↑ "Esophageal injury by apple cider vinegar tablets and subsequent evaluation of products" 
- ↑ http://www.apple-cider-vinegar-benefits.com/cleaning-with-vinegar.html
- ↑ Grandma was wrong!