I've been to Pump It Up in Pelham on several occasions and ALWAYS had a great experience. They are clean, organized, fun, and have a fantastic staff who seem to really like working there.
As for the review below, I don't think what she went to was a birthday party. It sounds like one of their open play sessions - where the facility is open to the public because ALL of their birthday parties are PRIVATE. It sounds like her friend just didn't want to pay for a party & decided to take the chance of inviting her child's friends to meet up at pump it up during one of their open sessions.
I've been there when they've had to turn people away because the maximum number of kids were inside because school was out. While my kids were disappointed, I appreciated their attention to safety. I would definitely recommend Pump It Up of Pelham to anyone who has kids.