Not exactly a representative sample, I know, but I have a PB/Poco Lena horse and from what I hear, he's typical of that line.
Classic old style QH confo - a witherless brick with legs, and a very broad back that takes an extra wide tree. Sticks at 14.2, rides much bigger. Small head with a kind eye and the tiny cat ears, wears a cob sized bridle. If you look at photos of him, photos of PB and photos of Poco Lena, you can definitely see the resemblance. The alpha horse in the herd, but quiet about it, doesn't kick or bite to make his point, a look is enough. Will try to cut or herd the tractor and the golf cart when they're in his paddock. Dead honest, will do anything you ask to do, all day long.
Smart, smart, smart - probably a little too smart for the taste of some riders and trainers. (I always think "stubborn" is code for "horse is smarter than the trainer") Adjusts brilliantly and appropriately to the skill level of his rider - will pack a beginner, take care of a tentative rider, and can be a blast for an experienced rider.
Now, this is the only PB bred horse I've know this well, but based on other's descriptions, he has a lot in common with other PB horses.
Based on him, I'd have another in a New York minute.