My trip from one nation's capital (Hanoi) to another's (Vientiane) was a long one: the sleeper bus took around 20 hours, plus another two hours getting from my hostel in Hanoi to the bus station. The trip was quite enjoyable actually - not least because the Vietnamese sleeper buses are the most comfortable ones I've experienced so far for overnight trips: their seats recline to about 150 or 160 degrees, which makes it possible to get a good night's sleep.
We arrived at the border at around 5:30 in the morning but were left to sleep until the border opened at 7 am. The border formalities were quick and painless, provided you were equipped with the right amount of US dollars and passport photos for the Laos visa on arrival.
My first impressions of Laos were the beautiful mountain scenery and the scorching heat at our lunch break.
Also, the houses in Laos seemed to be much bigger than Vietnamese houses. This might be correlated to Laos' population-to-land ratio: Laos is about two thirds of Vietnam's size, but has less than one tenth of its population. This means there is much more land to go around, which allows for bigger houses. There also seemed to be many more cars around. This could be due to a different taxation policy in Laos: with the 200% tax on car purchases in Vietnam, most people can't afford to buy a car; a different taxation in Laos would naturally lead to more cars.