It's a great concept but I don't think the numbers work out favorably. My recollection is that a growing southern pine forest can absorb about a ton of carbon per acre per year. The US emits something like 2 billion tons of carbon each year. The entire land area of the US is about 2.3 billion acres. About a third of that is forested already (if you take a broad definition and include scrub land as forest). There just isn't enough unused but currently unforested land to make much of a dent in our emissions.
I think biochar is going to be big. It's a cheap way to sequester carbon from agricultural/forestry wastes, and it provides a lot of side benefits from soil improvement to power generation. see Biochar - Wikipedia, the free encyclopedia
I think that biochar and improved agriculture and forestry each has great potential to play a minor role in CO2 offsetting. Several geology-based processes as well, but in most of those cases it looks like more cost/complexity. There are many possible contributors behind the largest and most obvious; energy use reductions. It makes sense to me to proceed rapidly on all fronts simultaneously. However broad economic slowdowns may put a crimp on that, and we may have to make due with less CO2 emissions caused by that for a while. However, I still can't think of a better way to climb out of a recession than by innovating energy-saving (and CO2 cutting) technologies that basically everybody is going to want to buy, as soon as they get a buck.
Here is a CBC science show look at biochar. http://www.cbc.ca/quirks/media/2007-2008/mp3/qq-2008-05-31_04.mp3 Put that into your mp3 player and char it.
