For many web developers is may be helpful to run multiple instances of Chrome to test multiple user types at the same time without having to constantly login and logout. Here are examples of how to do this by launching Chrome from the command line.
Ubuntu
chromium-browser --user-data-dir=/home/$USER/.config/chromium-profile-test
Mac OS X - Lion
/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --user-data-dir=/Users/$USER/Library/Application\ Support/Google/ChromeTest
There is much information about this here: http://www.google.com/support/accounts/bin/answer.py?answer=179236 but I found it easier to simple create a bash script to launch a separate testing profiles like so.
vim start_chromium_test_profile
Paste the following into the script file:
#!/bin/bash
chromium-browser --user-data-dir=/home/$USER/.config/chromium-profile-test
Make the script executable:
chmod +x start_chromium_test_profile
Run script:
./start_chromium_test_profile
Happy web developing!