The Pittsburgh food scene has actually built up some pretty decent places lately, as a food focused person that lives here, I hope that I can offer some places.
I agree with the other folks that Meat and Potatoes is good, food is good, but quite a trendy place and there are better places if you are looking for food.
Nine on Nine is nearby to there, and I think the food is great. Its gourmet American, nothing too innovative but well prepared food with good service.
Salt of the Earth is one of my favorites, is a farm-to-table focused place with a rotating menu, chef Kevin Sauza has been quite a hit here in Pittsburgh lately with pushing the Pittsburgh food scene. Would be one of my highest recommendations.
He also has a BBQ restaurant called Union Pig and Chicken which is not far away if you are looking for BBQ. I've been told by true BBQ snobs from the south that it is edible but will not compete with true southern BBQ.
Cure is in Lawrenceville, which is one of the trendy neighborhoods, and it has been a hit as well. I would highly recommend this place if you can get a reservation, they are known to be booked well in advance. No bar, BYOB (or BYOW), which is a feature I actually like.
Toast as mentioned before is in an odd location and you wouldn't suspect it from the outside, but great food and an excellent wine selection. Try the tasting menu with the wine pairing, quite a good value in my experience.
Root 174 is in an area called Reagent Square, quite a good restaurant that is small and not as well known.
Legume is in the Oakland area, recently moved from the exact location where Root 174 is now. Restaurant is good, but the bar next to it is even better if you like good cocktails.
Eleven, SOBA, and Umi have all been mentioned below and are part of one restaurant group here in town, Big Burrito group. These are all good, but I can't say I would recommend them for a visitor if you are looking to do food highlights of Pittsburgh. They are solid backups.
Can't say that any of the steak houses mentioned below are highly recommended. I really enjoy a great steak, but at this point have reserved that luxury for when I travel to cities that have great steak.
Finally, if you are looking for more "hole in the wall" places or ethnic places, let me know and I can offer some recommendations for that too. These would be my top picks for dinner for someone looking for good food in Pittsburgh.