One issue that has been ignored is that of security / confidentiality. What happens if the individual you are "courting" works for one of your competitors? Any project that he would work on for you would likely require access to sensitive, proprietary data. Sure, you could force him to sign an NDA, but that puts him in a strange situation post-project.
How do you balance giving the candidate access to your data such that he can work on a meaningful project (read: the results of which are actionable) vs. having him toil away with some dummy data just to see how he thinks?
There are often projects that need to be done in a company that aren't related to the core product, so it's not usually that difficult to give a contractor something unrelated to work on.
How do you balance giving the candidate access to your data such that he can work on a meaningful project (read: the results of which are actionable) vs. having him toil away with some dummy data just to see how he thinks?