It would be safe to say that Valentines Day is not a biggy in downtown Vientiane; as mostly an American greetings card manufacturer's legacy to the world - well having given it a big kick along (like many things out of America) it doesn't figure much in the Lao psyche.There is a certain amount of 'history' which should never be ignored!
So end of February will be just coming out of the wet season. Along with other young Lao's you will probably find there, a new walkway/park along the Mekong River is a great new spot to relax, take in the atmosphere and stroll. It extends all the way down to the Presidential Palace.
Treat yourself to a 'couple massage' perhaps at one of the upmarket hotels. Dine on the Mekong at a super-pleasant place called Kong View (recommended), a short tuk-tuk or taxi ride from downtown back toward the airport, then later take a supper club (as if you were in Paris) at a great place alongside the excellent
Hotel Khamvongsa called the Loft Bar (there isn't a loft - but a suave and large set of super comfortable couches and great service). Their cheese board is a genuine trip into 'village France'. Run by a French couple, their wine list is also worth exploring.
As far as entertainment, as I am not sure what day things fall in 2011 - make sure you seek out and take in the Lao National Circus. This very unheralded attraction is extremely 'cute'. Mostly acrobatics and a few performing dogs and monkeys it is a great look at what Lao families will do for an outing and entertainment.
Vientiane is often just a pass through for people, but as Asia's true boutique (as in small) capital it is worth spending a few days using it as a base for excursions.
Hope this helps. almost 7 years ago