Burning hydrocarbons...
I don't know if our descendants will curse or thank us for using hydrocarbons for combustion, but I would think it's a mix of the two.
take the inustrial revolution... they might have cut down a lot of trees, but without cutting down those trees they would never have been able to mass produce machines, which got them into the ground to look for coal, which then enabled them to drill for oil, which is what we are using today to fuel our transport systems, and is also what we are using to build solar and wind turbines now that we are getting to the end of 'easy to get to' oil (we'll have the black stuff for a few generations yet, but it will become increasingly expensive to get to as we go along...)
The thing to look at in this crazy development of fueling the development of a society is the effects that it has had. if we had never initiated the industrial revolution then we would not have the standard of living that we have today. Apart from flat screen tv's and computers, that also means medical treatment, science to understand the world around us (yes, it seems that we have almost eaten all of 'that' fish, we should probably ban the fishing of it for a few years to let stocks replentish - sort of thing).
Some people in the future will curse us for burning the oil, others will point out that if we hadn't started burning wood, making steam engines, mining coal, drilling oil and then proceeded to the next thing (wind, solar, fusion, bio, who knows) then they wouldn't have their 200 year life spans, a cure for cancer, faster than light travel, or the power to take care of our planet in a responsible sort of way (that is to say, keep it hospitable for our fragile meat shells, the planet does very good even during global warming/ice age, thank you very much).
But then again I am a optimistic realist :o) and I don't think we will ever completely run out of oil... at some point it will just become cheaper to get our power from other sources (yes, at some point wind energy WILL be economically viable without being effectively subsidised by oil), and we will stop drilling for it.
(I appologise in advance btw for my large leaps of logic, but this text field probably has a maximum length)