Come for lunch. The salad and peanut dressing are really, really, really good.
The main dishes are solid, and they are great at accommodating vegetarian and vegan requests. Good tofu; fresh veggies.
The only problem with the food is that something about the sauces (pad thai/pad see ew/etc) is off. They just seem to be a little sweet and runny -- maybe somewhat Americanized.
The service has also not been great on my last couple of visits. Nothing terrible, and I may have come near the end of the lunch shift, but I got the impression that the servers would rather chat with each other or finish their side work than come over and help me.
Still, come for lunch - you will get awesome salad/soup and entree with leftovers for a really good price. I crave Yuppha's almost every week.