they've sided with the US and didn't help them during the reovlution so they may have serious grounds for concerns. Iran has a historical beef with the US (and their shas) and the US doesn't easily forget it's failures - eg Cuba, and Iran. However China wasn't that much interested in securing global interests back then and that has changed dramatically.
Preliminary report: Palestinian stabs man near Damascus Gate, Jerusalem (Haaretz)
from the article: Netanyahu: WikiLeaks cables prove Israel is right on Iran