Visitors should be aware that Laos is not Thailand, or Malaysia, or Singapore. It is much less well-developed, having barely emerged from a Communist past. People are poorer, the sanitation is not as good, the chances of getting sick are higher. All that said, it is (possibly) the only country in SE Asia that bares any resemblance to what the region once was: culturally unique. To me, it reminds me a lot of the Thailand of the late 1960s, when I was first there.
Visas: Nationals of countries with money, i.e., the West and Japan, can enter the country without a visa at either the Freedom Bridge opposite Nong Khai (Thailand) or at Vientiane Airport. For US $50, cash they stamp in the visa and off you go. As I recall it was valid for 14 days. If you want to stay longer, visas may be extendable in the country; I would check at a Lao Embassy to make sure, however. Whether it is now possible to get a visa at Luang Prabang Airport, I don't know. It would be worth checking. Otherwise, you''ll have to get it in advance, and that means, almost inevitably, a stop in Bangkok.
The highway between Vientiane and Luang Prabang is still not finished; much of it is only dirt or gravel, so travel over it during the rainy season is problematic at best. Additionally, there are still occasional bandit/guerilla attacks on trucks and buses; hence, it's wiser to fly in or arrive on a Mekong ferry.
Most restaurants seem to be pretty safe; street stalls are very likely less so. I didn't take any chances. Having said that, Lao food is pretty interesting. I had a quite remarkable fish concoction that was rather like a French terrine that had been steamed in a banana leaf. It's not as fabulously hot as Thai food, either, so you aren't as likely to feel as if your head was about to explode after biting into an especially nasty Thai chili.
Because of Laos' French colonial past, you find baguettes and brioches almost everywhere, which is absolutely amazing considering where one is...