The Conservancy’s Program is actually going to involve a collection of individual projects focused on restoring and preserving specific areas using the funds contributed through voluntary carbon offsets.TNC is the right organization for carbon offsets -- they have, for years, used money to buy and preserve pristine land. If they sell carbon credits and use the money to set-aside even more land, then the additional money is really resulting in additional carbon-emission reductions (by preventing deforestation [past posts]).
The Conservancy’s trustworthiness shines out even more brightly because it actually offers a guide for what to look for in any good carbon-offsetting program: Permanence, Additionality, Leakage, and Standards (PALS). With all of this, you can feel confident in donating to The Conservancy’s Program, knowing that its work is credible and will be scientifically sound in each area addressed.
The key features are TNC's credibility as an organization that knows what its doing and its business model of preventing degradation of natural spaces.
Those interested in this topic should look at this recent post on TerraPass; in the comments, a co-founder of TerraPass says that their carbon offsets (100% made-in-the-USA) are also credible.
Bottom Line: Markets are starting to deliver reductions in carbon emissions. I am cautiously optimistic.