Google has officially announced on it's blog that it's now starting to report invalid clicks http://adwords.blogspot.com/2006/07/estimating-invalid-clicks.htm
They also offered official explanation why and how they are doing it.
"You can now run Campaign Performance and Account Performance reports featuring the number and percentage of invalid clicks that have been determined to be invalid and automatically filtered out by the AdWords system.
You are not charged for these clicks – the system's sophisticated detection and filtering techniques have identified these as invalid clicks and prevented them from being charged to your account. Read our FAQ about how Google detects invalid clicks to learn more about this process.
When running a Campaign Performance or Account Performance report, you can select columns within the Advanced Options section to include data about the number of filtered invalid clicks for the reporting period, as well the percentage of invalid clicks within the total number of clicks for the reporting period.
Please note that data for invalid clicks is only available for reports dated January 1, 2006 to the present, and that this data is not available for hourly views.
Here's how to run a report with data on invalid clicks:
Log in to your AdWords account.Click on the Reports tab and then on the Create Report link.For 'Report Type,' select Campaign Performance or Account Performance from the pull-down menu. Choose your 'View' from among the available options (note that hourly views are not available for invalid clicks reporting).Select the 'Date Range' for your report by using the time span. Data for invalid clicks reporting is available from January 1, 2006 onwards. For Campaign Performance reports, select which campaigns to include by choosing the radio button for All campaigns or the radio button for Manually select from a list ( to hand-pick your campaigns for inclusion). Within 'Advanced Options,' click Add or Remove Columns.Check the column option boxes for Invalid Clicks (for the number of invalid clicks filtered during the reporting period), and / or for Invalid Clicks Rate (for the percentage of clicks filtered out of your total clicks during the reporting period). Select any other data you want included in this report by clicking the appropriate boxes and adding filters if desired. Note that reports with data for invalid clicks can't include data for ad distribution.Enter a unique Report Name and check the box to save your settings as a template if you want to re-use them in the future.For 'Scheduling and Email,' schedule your report to run at regular intervals if you want it automatically generated; provide an email address for delivery if desired; and then choose your preferred report delivery format (.csv, .csv for Excel, .tsv, .xml, or .html). Click Create Report."
