Safari 5.1.2: FAIL
Safari 6: OK
Chrome 16.0.912.77: FAIL
Chrome 23: OK
Firefox 9: OK (uses mozDash)
IE 9, 10: FAIL
WebKit build 104795: OK
GeoGebra is believed to be the first major web application to make use if this, eg http://www.geogebra.org/web/milestones/dashedCurves.html.
And the GeoGebra developers were instrumental in persuading Google to implement this in Chrome. Visit the Google Code topic to read the whole conversation.