The nexus one can do pinch-to-zoom so of course it supports multitouch.
The hardware on the Nexus One was not designed with multitouch in mind. There was a firmware hack released that changes the way it reads the touchscreen hardware, such that it can "sort of" detect two touches. This hack fails when X and Y axes align, and it often loses track of which coordinates belong to which touch. Pinch zoom works because you're not generally pinching exactly down the axes.