So I decided to try to keep a record of all these "big bets" here - partly to help me answer the question, and partly to keep track so I can collect my winnings when I'm right!
Sara's Bet #1
Exercise will become incentivised within 10 years.
Stake: Whoever wins gets an actual hovering hoverboard.
Sara's Bet #2
National governments will cease to exist in 5 years time.
Stake: If I win, she votes for me for President.
Sara's Bet #3
We will use thumbprints for EVERYTHING in 2 years time.
Stake: £1. My mum hates betting.