Hashrate is starting to get a bit high for cpu mining to be effective at current growth rate. I got on with one of my old gpu's early on and am sitting quite a lot of them, but I have definitely noticed a drastic slowdown lately as the hashrates in general are skyrocketing.
You're right, the network hash rate is going to peak over the 10 GH/s mark very soon. CPU mining isn't the best way right now although I get around 40KH/s with mine so its still kinda worth it.