Carbon offsetting is one of the most disingenuous schemes for making money by falsely lightening people's consciences. It's only a few steps behind Bio-fuels, grown in the tropics on land which has been freed for this lucrative trade by slash'n'burn.
The aviation industry is the worst. Because people are focussing on CO2 rather than pollution, they give the false impression of making carbon neutral your weekend throwing up in shop doorways in Prague rather than Bradford - while getting away with pretending that the ground and stratospheric NOX's and the meteorological vandalism wrought by contrails don't matter.
Let's get this clear: crapping all over the planet and spending a few quid for someone to plant some non-native species of trees doesn't count. Consolidating your datacentre, then filling it up with blades which put some shitty animation in an unwanted browser pop-up is not eco-friendly.
Try saving your money or, better still, buying a gift from Oxfam Unwrapped, so an African farmer can put crops into his land, rather than the whole area turning into a dust bowl.