Google Chrome features an "incognito" mode that erases specified Web pages from its browser history and automatically deletes cookies when the incognito window is closed. While opening an incognito window usually requires a keyboard shortcut, some users have figured out how to launch Google Chrome in incognito mode by default.
Open your Applications menu and click "Apple Script Editor."
Click "File," then click "New." A blank window called "Untitled" appears.
Type the following code in the box:
do shell script "open -a Google\ Chrome --new --args -incognito"
Click "Compile," then click "Run." When you launch Google Chrome, it will permanently begin in incognito mode.
For Leopard users, use this code instead:
do shell script "/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome –incognito"