I'm running my crew through the last book of the Kingmaker series. The players consist of a paladin, rogue, monk, and oracle. When the oracle leveled up to 14 (CL 7), he gained the ability to Summon Monster VII and, therefore, the capability of summoning a Tyrannosaurus (Dinosaur).
Now, this is all well and good, but in practice, the tyrannosaurus has proven to be immensely powerful during combat. The combination of its to-hit bonus, damage, hit points, reach, grappling, and swallow capabilities make almost every encounter I throw at them unbalanced in the party's favor. Add to that the fact that the oracle can summon this guy 4x a day and place him almost anywhere in from the start of combat. Also add the fact that the oracle has not been adding the celestial template which would make the dinosaur even more powerful.
What typically happens in combat is the oracle summons the dinosaur on the other side of the enemies. The dinosaur then provides easily-accessible flanking to the party. The dinosaur then puts an abrupt stop to any enemy movement within 20' due to the threat of a free attack and therefore a grab. The grabs almost always succeed from the +32 grapple bonus. Then whatever creature the dino bit, is inevitably chewed on and swalled because the grabbed creature can't break the dino's CMD 39. All of these attacks work just as well against "boss" enemy creatures as well.
So is this overpowered? In our game it is, and I don't know the correct solution. Adding to the problem is that in the Kingmaker books, combats are one-offs. By that I mean, there are typically no dungeons and therefore a rationing of spells. Combats occur on different days and, therefore, everyone goes into battle fresh. Most combat also occurs outside also, so the dino has plenty of room to run around.