I’m quite a heavy user of Google insights. I find it a very effective way of comparing date ranges or keywords. From my own (admittedly pretty small and in need of refinement) analysis of insights data against the real world data, I saw a pretty strong correlation between the two. Sorry, I’ve got no numbers or evidence on that. Coast Digital did a study on the correlation and saw similar results. So overall, a pretty effective way of understanding what happened. Well, it was at least.
It seems that Google has significantly trimmed the amount of data they are providing through insights. Here are two screenshots from the results for the same terms, one made at the start of May and one made at the start of June:
To put in perspective how much granularity has been lost, these terms represent ~10,000 searches p/m.
I also tried another search for a term that represents ~2,500-3,000 searches p/m and was presented with this beautiful, detailed graph:
Google always presented some questionable data in the Adwords Keyword tool, because of their economic sampling and the way they bucket keyword volumes. Google Insights was one of the few places you could get some accurate, detailed data from Google, but for some reason they seem to have severely cut the data available. Is it cost cutting? Did they feel they were giving us too much information? Is it permanent?
Whatever the answers; if it stays as it is, then it is a big loss to data accuracy.