The peg is to the 7 day average price of Steem, not the price at any given moment. You can see what this price is at: https://steemd.com
At the moment, it's $3.44, but the price at Poloniex is $2.80, which is ~81% of the feed price. If the feed price is above the market price, SMD's will trade below $1. If it's below, it will trade above $1. Remember the fundamental value of SMD's is the ability to redeem it for STEEM at the feed price.
RE: Steemit For Investors #2 - How Steem Dollars Hold Their Peg to US Dollars - By Leon Fu Dot Com