Twenty years is a long time to look ahead...anyone in the UK of a certain age will remember Tomorrow's World on the BBC. The desktop will stay around for a while yet, if only in hybrid - ie. you plug your portable into it. But it has advantages that won't just go away: security, scope for greater power (and we will always want greater power), large screen viewing, and a keyboard. Damned if I can touchtype on a tablet for long - if only because its not good for your hands/wrists. (And for long periods, you need a well placed angled keyboard, and a good screen at eye level - honestly, it's not good for kids to spend all that time surfing, gaming, and doing homework on a laptop!)