I have NEVER heard that. I didn't hear it in 2007/08 and I haven't heard it yet in this election cycle. There are very few people in the US that don't know Hillary Clinton. She has a worldwide presence and is known by nearly everyone.
However, I've heard "Bernie who?" hundreds of times. I'll likely hear it thousands of times by the time the primaries come into full swing.
There is no plateau right now. The polls are essentially meaningless right now. Hillary has a set number of voters firmly in her camp and that's it. There are few if any undecideds for her to shift her way.
Bernie on the other hand has millions yet to get to know him. He has millions struggling day to day that need to hear his message and will embrace his platform as soon as they hear it.
We've just started this election. GOTV, get out the message, and stay positive.
An easy thing to do is to print and hand out flyers. Many can be found here:
http://feelthebern.org/
Scroll to the bottom of the page for pdf downloads of flyers you can hand out. I find them to be a big hit at the drive thru window.
(Thanks and credit to Retrowire for the link)
Bernie 2016. We have voters to find and get motivated.