I can vouch for this. Been with PN since 2013 and only had 1 minor problem and that was with a certain router. They sent me a replacement in a few days and everything's been great since.
I've also used their Live Chat feature as well as their forums and they've been excellent.
On the topic of retentions, I was amazed at how quickly they agreed to continue the reduced rate of BB. I've been paying £2.50 a month for about 15/16 meg which is more than enough.
So a pretty massive applause from this corner here