The previous reviewer was correct in that the service at Vientiane is pretty lousy. But if you're prepared for it, you can be proactive and not let that ruin your enjoyment of what is pretty good food with generous portions at a great price.
First off, don't wait for the one waitress (there is rarely more than one) to come to you. Ever. Once you're seated and ready to order, just go up to the counter and order. Then ask for a pitcher of water (you will most likely go thirsty if you don't). Once the order is in, the food usually doesn't take long at all. Just remember to be proactive and don't let her ignore you. If you take my advice on this, the bad service that others around you are getting almost becomes comical.
And I concur with a previous review. This is the ONLY place in Madison that I don't go four stars. I did it once and I ate the whole dish, but it was not very enjoyable. It was insanely hot, and I have a really high tolerance for heat. Unless you're like me and most places are just never hot enough for you, go with three stars maximum, probably even fewer. My girlfriend has a decent tolerance for heat and she usually just gets one star. Don't be a hero!
With these things in mind, I think you can enjoy the experience. Pretty good food and lots of it for a very fair price (especially at lunch). Just make sure that there is no fish sauce in what you're ordering (unless you're into that - ewwww).Pros: super spicy, cheap, big portions
Cons: bad service