Although Google has perfected the search engine (or at least made it very very very good at finding exactly what you need), it’s still far from being able to suggest relevant ads on Gmail. I constantly see links inviting me to get a PhD online or to evaluate my chances of getting into MIT. Note that Gmail knows I have an MIT email address and my signature contains the words "PhD student”. Maybe they’re afraid of using that information for privacy concerns?
Also, I’ve been getting links to recipes using Spam (the meat) for a long time. I could not figure out why. I thought maybe Spam was launching some advertising campaign and paying Google tons of money to put links on Gmail. It’s only a few days ago that I realized the Spam recipes come up when I check the message in my spam folder. Really, Gmail? Really?