I agree with Chuck S.
Chaya is absolutely the best Japanese restaurant that I've found in Pittsburgh. The place is really small and cozy so that it doesn't feel like you're in a chain restaurant. The service is excellent, quick and friendly.
Oh, and the sushi is amazing. The amount of rice that the chef uses is perfectly balanced with the size of the fish. It's not a bloated rice ball with a small piece of fish. The rice was perfectly packed so that it was solid, but airy enough to come apart easily when you bit into the nigiri sushi. The rice was not too vinegary as I've found in a lot of the sushi restaurants in Pittsburgh.
Also, the menu is quite authentic and has many choices that you wouldn't see at the majority of restaurants in Pittsburgh. They have onigiri balls, nabemono and much more.
Expect to wait a bit if you go at peak times. It is a small place that has about 8 tables and a sushi bar that fits 4 people. However, it is definitely worth the wait. Also, the BYOB is great allowing you to bring in your favorite beverage. Corkage is $2 per glass for wine and beer I believe.
Prices are very reasonable. For two people, it cost me about $50 with the tax included. We were able to get the deluxe sushi dinner and the sashimi dinner combo. The dinner combos came with your choice of edamame or fried chicken (common bar food in Tokyo) plus salad and tsukemono. You would be paying the same prices at another sushi restaurant on Walnut or in the Waterfront and the fish is not as fresh or delicious.