Hmm, I go up to Pittsburgh at least three times a year, but I've never been to Primanti's... Something to try I guess.
And yet, you never call...
Primanti's is great, but you should try one of the new locations in the burbs as well as one of the original 3 in Pittsburgh. One is downtown in Market Square near the PPG building, one is in the Strip District (John McCain ate at it yesterday or the day before), and one is on the South Side on Carson Street... The original places have a charm the new "suburb" Primanti restaurants do not have. They also have significantly smaller menues though. That's why you should also check out the suburban ones... Monroeville, Greensburg, Cranberry, Harmarville (the one nearest me I go to routinely), etc. all have one now that is a large restaurant/bar and a much fuller menu with pizza, regular sandwiches, etc.
Basically a Primanti sandwich is a sandwich on thick white bread with fries, coleslaw, and tomatoes on it.... all on one big sandwich. Now, personally I hate slaw and tomatoes, so I get basically just a sandwich with fries on it, which they'll do, but you really haven't had the primanti experience then.
If you're into BBQ, try Buffalo Blues in Pittsburgh's Shadyside... it's a trendy/youthful area near Oakland/colleges. Buffalo Blues rocks and is where I gained too much weight in the last 5 years.
Best Japanese Steak House in town is Nakama on the SOuth Side and that's become a yearly tradition for me to take my gf there for Valentine's. We ate at Evgani Malkin's table the year before last, so basically we sat with him and his interpreter family the whole time. Pretty neat. Great Sushi and great food in general... Pricey kinda, but not too bad. There's a ton of those types of places that have cropped up in the last 5 years, and every area has one, but the Nakama is outstanding and surpasses the rest.
If you're looking for super elegant... Pittsburgh Rare in the Sheraton Inn Station Square is outstanding, The LaMonte on Mt. Washington is Oprah Winfrey's favorite restaurant (supposedly) and is insanely expensive (I only ever ate there with my family's lawyers), and also in Station Square is the historic Grand Concourse... The GC is on historic Smithfield Street just off the Smithfield street Bridge (a very old bridge), and it was the old Train Concourse in Pittsburgh so it's a really interesting building. There's in and outdoor seating, and a bay window seating area that's very romantic and looks at downtown Pittsburgh from the other side of the Monongehela River (but down near the point where all 3 rivers converge).
I've eaten at all the above and find them fantastic. There's an Irish place on Carson St. in the South Side I can't recall the name of, but it's my favorite Irish place... There's a fantastic Steak place too I hear on the SS called the Pittsburgh Steak Co., however I've yet to eat there. I hear great things about it too though. For bars, you cannot beat the South Side. It's nothing but a maze of small hole-in-the-wall type places, clubs, restaurants and more. Loads of people go there, but there's barely any parking and it's all on the street. It's an old community and something neat to see though, especially if you're from cities out west where the old tight/confined city streets situation aren't exactly like they are in older cities in the East.