An absolutely incredible trail. It's included on all of the internet's lists of greatest long American bike trails. It's an ideal trail for bike tourists. It's very flat so you can cover a lot of miles in a day and there are frequent camp sites (both free and commercial, primitive and luxury). Its fairly well traveled so you know there will eventually be someone passing by if you get into trouble, but you can also go for miles without seeing anyone which is nice sometimes. I've always felt safe riding on this trail which is important for a solo female rider. There are frequent bathrooms and water sources (not all water pumps provide potable water so bring some sort of purification mechanism if you're embarking on a multi-day ride). There are towns all along the trail which means options for diner meals, grocery stores, bike shops and a few cute little tourist attractions.
Most of the trail is crushed gravel which means a little tread will be an advantage. Any bike is really going to work just fine. I ride a cyclocross with 700c tires and am perfectly comfortable riding this trail. Some parts can get really muddy and in those circumstances I envy the mountain bikers.
This trail is great for short day rides or multi-day excursions and Pittsburgher's are lucky to have such easy access to such a great biking route.