I wouldn't put it past the bloody Brits to use something as esoteric as stones, but I've heard plenty of UK people use kgs. Maybe it's the crazy Irish people.
*looks up encyclopedia entry*
Current use
Although no longer an official unit of measure, the stone remains widely used within the British Isles as a means of expressing human body weight. People in these countries normally describe themselves as weighing, for example, "11 stone 4" (11 stone and 4 pounds), rather than "72 kilogrammes" in most other countries, or "158 pounds" (the conventional way of expressing the same weight in the United States). Its widespread colloquial use may be compared to the persistence in the British Isles of other Imperial units like the foot, the inch, and the mile, despite these having been entirely or partly supplanted by metric measurements in official use (a similar usage persists in Canada, despite that country, unlike the USA, having converted to the metric system in the 1970s).
The official unit of body weight in medical and other contexts is the kilogramme. In official use, provision is usually made for the public to express body weight in either stone or kilogrammes. For example, on at least one National Health Service website both Imperial and metric units are used [3].
Outside the British Isles, stone may also be used to express body weight in casual contexts in other Commonwealth countries, particularly Australia and New Zealand.
Though not predominantly used in media, the Ultimate Fighting Championship weigh-ins on European based pay-per-view channels use this measurement to show the fighter's pre-fight weight.
A stone is also a measurement of weight in the game Ultima Online.
http://en.wikipedia.org/wiki/Stone_(weight)