I stole this method from Mike Gullo a Product Owner working for CareerBuilder at the time.
The premise is simple you may have a prototype or a card sort exercise, maybe you've interviewed your users and documented a list of pain points. Basically, you have a collection of things and you ask them to add values to them using the monopoly money provided.
This simple system allows users to attribute value to things in priority order. It's useful when you are looking to understand how users perceive their pains.
Bigger denominations equal more weight on that item. Users can put as many notes on a single item if they so wish. Any items without a note will be discarded at the end.
The playful exercise makes for a nice antidote to user sessions which can often be void of stimuli. Users always get excited by the prospect of playing what they think is going to be a game. More on that later.
Because monopoly uses currency it can help people think in terms of real costs and return on investment. While the suspension of belief isn't as perfect as the real thing, it is a whole lot cheaper.
When users get into the activity itself they quickly establish they can prioritise 1 or 2 things or spread the notes across many things. But they'll always be forced to prioritise one thing over another as the denominations of monopoly money enforce this.
This can actually become quite a stressful time for a user as they weigh up the pros and cons of each thing and start to make judgement calls on what makes the cut.
UX is like a joke. If you have to explain it, it's probably not that good*.