I refused to do a take-home interview exam for the first time a couple of months ago. I don't think a $100 gift certificate would have made much of a difference. The opportunity was a decent one but I've just had very bad experiences with take-homes in the past (spent a lot of time, didn't hear back for a month, got a one-sentence rejection from a recruiter, never talked to a developer). I might consider doing it later in the process, when I have a stronger sense that the exam will be taken seriously and given proper consideration. I'm just not willing to put this kind of time into what may simply be "screening".

I think Gayle Laakman McDowell's comments on this subject were good:

http://www.gayle.com/blog/2013/09/18/companies-who-give-cand...

The problem here is that take homes allow companies to externalize the inefficiencies of the interview process - they may demand many hours of a candidate's time while dismissing that candidate in five minutes. The $100 gift card may make this a bit better, but it's still a bargain for the company (I'm certainly not surprised you consider the information easily worth $100).