What donnah said.
The first "surge" is followers who are notified you published a hub, your hub being displayed in the "new" section etc. After a few days that drops off. It can take 6-9 months for Google traffic to pickup to decent levels (if you have a not too saturated topic with good keywords.)
You can create Made for Pinterest images to help you drive traffic from Pinterest, but social bookmarking sites (Digg, Reddit etc) are basically spam pools that give short bursts of low quality traffic.
Linking your own hubs on Facebook is likely to make your friends feel spammed too.