I just downloaded the new Google Chrome for Mac beta. I like to clear out my cookies after each time I quit the browser, so tracking information and so on doesn’t hang around any longer than it needs to.
On Google Chrome for Mac, there is no built-in setting to force all cookies to be session cookies, but you can use this hack to achieve the same thing. After launching Chrome at least once, then quit it and run the following commands in Terminal:
rm "~/Library/Application Support/Google/Chrome/Default/Cookies"
ln -s /dev/null "~/Library/Application Support/Google/Chrome/Default/Cookies"
The first command deletes the cookies file and the second command creates a symbolic link, so that anything dropped in the cookies file goes to /dev/null (i.e. the cookies gets deleted and not stored once you quit!)
UPDATE 2010-01-29: JeanVal reports in the comments that this process works on Chrome for Linux too. The Cookies file is stored at the path ~/.config/chromium, so just adjust the commands above to fit that path.