I do either or both depending on my mood. Like virginian said, I too pedal to give that extra oomph at high speeds. Unlike some others who posted here, I don't usually use the pedals uphill -- that's when I like to sit back, relax, and let my electric bike do all the work for me
When I'm commuting, I tend to not pedal because I don't want to sweat. When I'm site-seeing or traveling, sometimes I like to do both because I'm usually going at a somewhat slow speed and pedaling slow isn't an added burden.