We used IPT to get our doggy over. We had the extra complication that we left the US before our dog did so we had to use a shipping company to help with the logistics. IPT were great in this respect. They worked everything out for us, told us when to do what (which is especially important in those last 30 days, as egnz points out).
Maddy got here just fine. She travelled really well and is now relishing her freedom after quarantine. I would say that IPT weren't great at the "touchy feely" stuff. For instance I was incredibly nervous about the whole thing and would have liked to have received lots of reassuring emails. I got an email that she'd arrived in LA safe and well and that they had her (she was boarded with them overnight following her flight from CT). They said they would email me an update the following day when she arrived in NZ. I heard nothing. I've never heard from them since. Yet their website makes out they understand your pet is part of the family.
In terms of costs, I think we paid IPT around $1,700 for their services, which included Maddy's flights to Wellington. On top of that were all the vet appointments and her flight from CT to LA, quarantine is additional, so we probably paid about US$3k in total to bring her.