If someone has built a sneak attack deck properly and gets to go first, the opposing player is taking at least 7 damage on turn one, and losing their hand. It's very very tough to come back when you're top decking the whole game.
Oh, and Kathleen, if you want to make an infect deck to take on the masses (extended deck), look into the three cards: Snake Cult Initiation, Virulent Sliver, and Hivestone. Add more poison to all your critters and make them suffer. (These all will work in your deck as long as it's Green/Black.)