In their Friday blog, Google announced they have launched a new feature in the AdWords interface, Impression Share - the percentage of impressions your ads see. Thus giving very accurate numbers for total searches for all keywords or their expanded matches.
The feature is well detailed by the Googlers.
Meet Your Favorite Search Engine Watch Contributors
Many of SEW's leading expert contributors will be at ClickZ Live, the new online and digital marketing event kicking off in New York (March 31-April 3). Hear from the likes of: Thom Craver, Josh Braaten, Lisa Barone, Simon Heseltine, Josh McCoy, Lisa Raehsler, Greg Jarboe, Dan Cristo, Joseph Kerschbaum, John Gagnon, Eric Enge and more!