Speaking for myself, I'm happy to volunteer for small non-profits, because they really need it, and ten minutes of my time can really make a difference (I just translated a 100-word paragraph about an award from German to English, for example).
But Sparked themselves are a for-profit venture. I'm not 100% sure that's going to be viable, but I'm not willing to give them my time for free if they're going to turn around and make money off it.
"Re: business model. We make money by selling the platform to corporations as a way to manage their employee volunteering programs."
Non-profits do not pay to use the platform or for any tasks completed. Large companies pay an annual fee to enable access for their employees and related reporting metrics.
The parent comment to my comment was to the effect that they could use the microvolunteering concept for their own development. To a certain extent, I could even see volunteering for them (getting the word out or something), but I personally would draw the line at actual technical work for free for a money-making venture, unless there were public karma attached or the code in question were open-sourced or something.
But Sparked themselves are a for-profit venture. I'm not 100% sure that's going to be viable, but I'm not willing to give them my time for free if they're going to turn around and make money off it.