If BlackBerry's comeback fails, the PlayBook will be remembered as one of the nails in the coffin. Research in Motion was so busy showing off that it's 7-inch tablet could play high-def videos via its HDMI port that it forgot to include native email and calendar apps. That's right, the PlayBook didn't let you view your messages or appointments unless you had a BlackBerry phone connected to the slate via Bluetooth. Amazingly, RIM called this glaring weakness a security feature. Less than 9 months later, co-CEOs Mike Lazaridis and Jim Balsille stepped down from their posts.