Actually you stated "the productivity enhancements of a tool you really know far outweigh the price of it", which is wrong if you have zero money. With zero money Gimp will always reign supreme.
I don't necessarily know that that is an insult, but sure, if you're short on cash then free is always better and certainly beats piracy. I was thinking in terms of professional tools, and the output value delta of something you know well (this might just as well be the Gimp) compared to unfamiliar software.
If you're a professional though you don't exactly have "zero money". The amount spent on a DSLR alone is bigger than what you'd spend in a Photoshop license.
The only way that would make the GIMP an alternative to photoshop would be for your time to be worth NOTHING.
