While I don't think that carbon offsetting is going to solve any long-term problems, it is nice to plant some trees and have a bit more money poured into renewable energy research.
We're not going to see real change until we are out of coal and oil. Hopefully that will happen soon. (Yes, it will be painful. But the sooner the pain starts, the sooner it will be over with.)
"At the current production rate, [coal reserves] would last 164 years."
"According to the widely accepted view, at current production levels proven coal reserves will last 155 years (this according to the World Coal Institute). The US Department of Energy (USDoE) projects annual global coal consumption to grow 2.5 per cent a year through 2030, by which time world consumption will be nearly double that of today."
From: http://www.energybulletin.net/node/29919
The article goes on to say that we probably don't have 155 years of coal reserves, but it should still last for some time now, unless the rate of usage sky rockets.