I've spent many an afternoon/evening at the Walnut Grove in Waterworks - mostly for happy hour, but sometimes for dinner as well.
The happy hour is pretty decent. Although the prices have gone up since I last visited. About a year ago, the ahi tuna was included on the half priced apps for happy hour menu. For $5 you could get a nice sized piece of tuna - but it seems they caught on to the fact that they probably weren't making much money.
The service is usually OK - nothing special, but not awful either. The one issue I have is that I just don't love their menu. Some overpriced salads, a couple of pizzas - 2 are pretty much identical except for the addition of fries (it is Pittsburgh people, fries come on everything!). A small sandwich selection and some seemingly overpriced entrees.
I'll give them 3 stars for happy hour, but maybe 2 for the menu and pricing. But it's a convenient location and an alternative to heading downtown or to Lawrenceville when I'm in town and staying at Bakery Square.