I'm trying to find out, how many sites Google finds for a given keyword. Right now, I'm using Google's AJAX API and check the estimatedResultCount variable in the response. But it seems like this number greatly underestimates the number of hits. For example, one of my test keywords has > 250.000 hits in the normal Google search but only 3.540 when I use the API.
Any ideas what I could do to improve my results? Or is there maybe another way to get this number?