The second way they generate traffic is golden egg hunts. Basically, they hide "golden" egg items in their posts. At first, whoever found these first won the items. This is awesome for people who know about the site, but leaves no reason for people to tell their friends (more people = more competition). Also, some stanford kids were caught for "cheating" - using java scripts to pull all the images down from the website and then comparing hashes to find the golden eggs. The "added security" for this was what they call "requirements" for winning an item. These have ranged from awful (email 100 friends about chegg 1st to win a Wii) to fun (various puzzles). The site is influenced a lot by user suggestions also, (ie someone complained about spamming people to win prizes and they pledged to never do email reqs again) which is interesting in itself.
The real question is, "How does chegg make money?". No idea here. Also, how did these kids get $2 million in investment capital? The website interface and security suck. Also, items have been shipped to me with a decent amount of address info missing from the envelope and the stamps are not your standard "printed from the USPS postage", but actually a collage of stamps with varying postage ($.02, $.37, etc), like they had rifled through their parents drawers looking for stamps. All in all though, I have won some great swag, pictured here, but also recently received a Wii.
Ha.