Lao currency is called kip (LAK). The exchange rate is around 8,000-9,000 to US$1. US cash and Thai baht is commonly used for larger purchases. Kip is a non-convertible currency, meaning once you have left Laos, it's useful only as wallpaper. Banks outside Laos will not accept nor exchange kip. International access ATMs dispensing US dollars can be found in most major tourist centres across the country.
Despite being one of the poorer nations on earth, Laos is a very safe country to travel in. Petty theft, particularly the snatch and grab variety, is a bit of a problem, but only really in the capital Vientiane. Drugs are readily available in some centres, notably Vang Vieng. Partakers should exercise a great degree of care as overdoses and deaths are not unheard of -- not to mention buying is illegal.
While corruption is an issue in Laos, the police can be of moderate assistance. Don't expect to be extorted as may happen in Cambodia. Most police will not speak English.
Anything more serious than a papercut or a hangover, get to Thailand for seriously good healthcare. Do not, repeat do not, undergo any serious medical treatment in a Lao hospital if you can avoid it. You have travel insurance right? This is what it is for.
Public transport is relatively comprehensive and inexpensive, but very, very slow. Driving standards are woeful and seatbelts are close to non-existent, but speeds do tend to be slow. Motorcyle taxis are a very common way to get around -- always wear a helmet (if you can get your hands on one). Road quality, especially in the mountainous north, can be very patchy and in wet season landslides are not uncommon.
Yes, you will need a visa for Laos. See our Laos visa page for details.
If you already speak some Thai, you'll find the basics of Lao not difficult to pick up. The two languages are related, but not all that close -- think Spanish to Italian rather than Spanish to French. Lao speakers tend to understand more Thai than Thais understand Lao, though that may have something to do with Lao being better listeners (and the economic underdogs)!
There are two seasons: the hot dry season and the hot wet season. Chances are if you're from anywhere outside the tropics, you'll find Laos to be very hot -- and sweaty. For detailed weather info, see our Laos weather page. The exception is the far north, especially Phongsali province, which can get downright cold, especially in the evenings.
Laos is a developing country
Don't expect the bus to leave on time, nor for your mojito to have ebough mint in it. The tourism industry is developing and considerable resources are being poured into training, particularly in Luang Prabang, but it will take time for Laos to really shine. Outside of the main tourist centres, don't be surprised by the complete lack of tourist infrastructure.
Laos is a wonderful country
Don't let the slow buses put you off. Laos is a fascinating destination. It takes a long time to get around -- especially in the north -- so don't try to bite off more than you can chew. In Laos, less is more: See fewer places for longer stretches and you'll have a better time.