So, when looking for opponents for a level 1 party, you can use up to level 5 monsters without any problems. You can go even higher for hard encounters.
Eh, in my 4e group's first encounter, seven level 1 PCs, I nearly wiped them out with: 1 Hobgoblin Lieutenant (level 5), 1 Hobgoblin blaster wizard, forget the name (level 3 artillery/controller), 1 hobgoblin archer (level 3 artillery), and maybe 4 hobgoblin grunt minion-3s. 5 level 3 opponents would certainly have smushed them.
They were able to handle groups of 6-8 grunt minions led by 2-3 level 3 soldiers & artillery though.
Edit: If I start another 4e campaign I think I'll start at 3rd, so beginning PCs can face the mighty Hobgoblin Soldier or Orc Raider without peeing their pants.