Vs. http://www.alexa.com/siteinfo/news.ycombinator.com
Note that Alexa also shows 35% of inbound search traffic for HN is hacker news, but only 6.5% of slashdot's inbound traffic is from the slashdot term. So comparing the two terms to each other short changes slashdot.
As a CS major at Berkeley, it's hard to find a tech major who isn't thinking about going into startups, unless they're going into Finance.
Unless you're talking about a sophomore in high school, but for some high schools HN is still fairly well known. I'm definitely in a minority sample here, though, considering that a significant amount of people in my high school friend group dropped out of college to do startups, are Thiel fellows, are working at various tech companies in college, etc.
I wouldn't expect it to be outstanding for either site.