My friend when China was isolated by the world, Pakistan facilitated Nixon's visit to China in the '70s. Pakistan has since supported China on every issue of importance to PRC and even introduced China to the Muslim Bloc by using whatever, though not substantial, influence that Pakistan has or rather had, with Muslim Countries.
In return China has stood by with Pakistan when it mattered the most. Whenever we were isolated in the world...even our so-called Muslim Brothers abandoned us or refused to recognize us...China never backed down and always stood by. When at the back-drop of the OBL raid in May, last year...when the US was eyeing us aggressively, China provided invaluable diplomatic support. She has invested in infrastructure projects all over Pakistan at minimal profits, sometimes at cost and at times by giving us pretty soft loans. Our military cooperation is on a complete different level and we both support each other on international forums where it matters the most. They have never arm twisted us to do anything, never blackmailed us or exhibited ill will towards Pakistan. I'm not sure why Vietnam-China relations went down hill but I, as a Pakistani, have followed China-Pakistan relations quite closely and have interactions with the Chinese and by God...I consider them our dearest friends.