Latest version: 0.2 (download link below)
I have quickly put together a Windows app which takes the location/time data from your iTunes backup and turns it into a KML file. Just double click to open in Google Earth. Alternatively it can produce a CSV file for importing into a spreadsheet.
This is inspired by Pete Warden's iPhoneTracker application.
.NET Framework 3.5 is required. You can download that here. nphonetrack comes in a 7zip archive, which you can open with 7zip or Winzip. Just extract the archive and run nphonetrack.exe on the PC you sync your iPhone to.
Like Pete's app, the points are not reported exactly in this app. They are quantised to roughly a 3km grid, and the dates are rounded to the nearest 7 days. The real data has greater precision in both location (although the points are not necessarily accurate) and time.
0.1 Initial version
0.2 Resolved issue with SQLite interop assembly not loading under some circumstances - switched to older version of SQLite
Pete Warden's iPhoneTracker application
Python script found here