I don't know which nightly build did it, but some time in the last week, Webkit hit 100/100 on AcidTest3.
Just went there myself to see with last night's build.
http://acid3.acidtests.org/As far as I know it's the ONLY browser that manages a perfect score. Apparently there is an internal beta of Opera that gets 99, but the publicly available beta of 9.5, build 4506 only gets 61/100.