My first thought: Why should a forum user appreciate the masking of all external links? And so, why should a forum owner install such an extension?
Then I clicked and read your link and realized that it is even worse. Not only do you mask external links, but you also annoy your users by making some money out of them (via advertising, I suppose). And the cents that the forum owner earns certainly compensate for the quick exodus of their users.
A perfect loose-loose strategy, but wait ... at least Exobucks makes some money without paying dearly.