Korean Money Matters
The currency of South Korea is the won (₩), written 원 in hangul. As of March 2009, the exchange rate was approximately 1500 won to the US dollar. You can check the exact rate at XE.com
Coins come in denominations of ₩10, ₩50, ₩100 and ₩500, while banknotes come in denominations of ₩1000 (blue), ₩5000 (red) and ₩10,000 (green). ₩1 and ₩5 coins, while they exist, are very rare. The largest bill currently in circulation is only ₩10,000 (US$7, €5), which makes carrying around large sums of currency a bit of a chore. However, a yellow ₩50,000 banknote will be introduced into circulation in June. ₩100,000 "checks" are frequently used, and some of the checks go up to ₩10,000,000 in value. These checks are privately produced (by banks, etc.) which can be used as "c-notes".
A new series of notes was released in 2006/2007, so expect to see several versions floating around, and be prepared for hassles with vending machines which may not accept the new or old versions.
ATM are ubiquitous, but most Korean ATMs don't accept foreign cards, only special Global ATMs do. These can be found at airports and some subway stations in major cities, as well as in many Family Mart convenience stores, so stock up before heading to the countryside. Citibank cashcard holders can withdraw in every Citibank branches(ATM) in South Korea with charge of US$1 and check balance of checking account for free.(Chinese, English and Korean services are available on ATM.) Credit card acceptance, on the other hand, is very good, and all but the very cheapest restaurants and motels will take Visa and Mastercard. (It is illegal to refuse credit cards unless it's a very small shop)
CostsKorea is fairly expensive for an Asian country, though notably still cheaper than Japan. A frugal backpacker willing to eat, live and travel Korean-style can squeeze by on under ₩60,000 per day, but if you want top-class hotels and Western food even ₩200,000/day will not suffice. Seoul is particularly expensive, by some measures even more so than Tokyo.
Tipping
Tipping is not necessary anywhere in Korea and could be considered offensive if you try to do so, except maybe bellhops in high-end hotels. Tipping is not the norm, and is a foreign concept. An exception to this are bars which have large crowds of Westerners, and you can expect tipping culture to be exactly like westernized countries. Maids in hotels appreciate 1000-2000KRW tips as well, and you will often find additional towels, soaps, and things of that nature should you leave one. While not necessary, almost no one here (or anywhere) dislikes receiving additional money.