About a month ago, Google's external keyword tool began to show search volume numbers. Last night, there were reports via WebmasterWorld that the tool stopped showing these estimated search volume numbers, all together.
The reports were sending back error messages that read, "Insufficient Data." This happened for any and all keywords searches between the times of about 5pm (EST) and 10pm (EST) last night, August 5th.
I personally tested the tool this morning and most popular keyword phrases are showing search volume data. I suspect it might have something to do with the launch of Google Insights for Search, which Tamar will have a post on later and which I wrote about at Search Engine Land just about 8 hours ago.
All seems to be good now with the Google Keyword Tool.
Forum discussion at WebmasterWorld.