2. Email is for old people

Those early adopters who were so cool because they used email are now in their 40s -- or 50s, or 60s, or even 80s! As every parent knows, if you want to reach your kid, email is not the answer.

Yes, the population of email users is aging. But the situation isn't quite as bad as it seems, according to Forrester Research. Forrester data from Q3 2008 shows that 92 percent of online adults (those 18 or older) in the U.S. use email daily. In the 12- to 17-year-old set, however, less than 50 percent check their inboxes at least once a day.

"As young people age, their email habits start to look a little more like those of adults," says Forrester analyst Julie Katz. She thinks this is partly because email is so entrenched in workplace culture.

OK, but even if office workers learn to "live in Outlook," are they opting in to marketers' messages on the work email? Probably not -- or, at least, only for B2B offers. As today's teenagers enter the workforce in a few years, Katz warns, "We'll see a shift to social media -- and marketers will need to find a different way to reach this population."