Well, impressions don't usually jump (unless you suddenly got a very good link on some popular website, or got stumbled on stumbleupon) - gradual growth is good enough for me. But do make sure you keep building content, and keep promoting the website. Growth will come, if you do that, whether in jumps or gradually - who cares? There are going to be slumps as well. Don't let that stop you (if you do: traffic will stay down; if you keep building, likely traffic will go up again). These things go up and down. Don't spend too much time worrying about it.