Whatever happened to Henry George's ideas? I have heard that Henry George wrote one of the biggest selling economics books in history (Progress and Poverty) and was so famous that 100,000 people attended his funeral, and yet his ideas about land are nowhere to be seen in most economics textbooks. Why is this? Were his ideas thoroughly rebutted?
If you're referring to a land-value tax, I'll just quote The Economist:

Other economists like it too. Adam Smith said “nothing could be more reasonable”; Milton Friedman termed it “the least bad tax”. Winston Churchill said scornfully that a landlord “contributes nothing to the process from which his own enrichment is derived”. The Organisation for Economic Cooperation and Development, a Paris-based thinktank for industrialised countries, supports the idea. So too did a recent working paper by the International Monetary Fund and the Mirrlees Review of British taxation by the Institute of Fiscal Studies. The mayor of New York City, Bill de Blasio, hopes that taxing vacant lots by value will help deal with urban blight in the Bronx and elsewhere.
[...]
The idea has wide-ranging support among modern economists, and more than 30 countries have some form of land-value taxation, usually in harness with other property taxes, on buildings.

While the idea of a land-value tax certainly has its drawbacks, it's far from being discredited.