In the long term, the GPL kills the major incentive to improve the software's design and feature set, even though small improvements and ports may be made.

Sprinkling the GPL on top of a project no one wants anyway does nothing (I say this from experience), and applying it to a popular program just holds it back (by keeping it from getting the cash that people would otherwise pay).

As an end-user, I want to see Light Table take off, and to continue innovating, not to continually engage in campaigns for donations.