I found various places:
C:\Program Files\Steinberg\Cubase 6\VSTPlugins\Synth
C:\Program Files\Steinberg\Cubase 6\VST XMLs\Steinberg Media Technologies\Embracer
C:\Program Files\Steinberg\Cubase 6\VST XMLs\Steinberg Media Technologies\Monologue
I found various places:
C:\Program Files\Steinberg\Cubase 6\VSTPlugins\Synth
C:\Program Files\Steinberg\Cubase 6\VST XMLs\Steinberg Media Technologies\Embracer
C:\Program Files\Steinberg\Cubase 6\VST XMLs\Steinberg Media Technologies\Monologue