I use this activity with my gifted students as a challenge activity in which they develop a problem/question of their own using critical thinking skills.
Last year, the ideas ranged from "How can I become an expert jewel thief?" to the more typical "How can I best go about getting straight A's during 6th grade?"
As part of the activity, students must think through their ideas, no matter how imaginative, and identify the main steps of any valid experiment (i.e. identify IV, DV, control group, constant, big question, hypothesis, and conclusion).
I use the ideas generated by students for labs throughout the year if they are able to be easily performed in the classroom in order to reinforce the concepts we've covered about the scientific method at the start of the school year.