Arduino does not start and complains of the following error:

Uncaught exception in main method: java.lang.UnsatisfiedLinkError: /Applications/arduino-0016/Arduino 16.app/Contents/Resources/Java/librxtxSerial.jnilib: no suitable image found. Did find: /Applications/arduino-0016/Arduino 16.app/Contents/Resources/Java/librxtxSerial.jnilib: no matching architecture in universal wrapper. To fix this, click on the Arduino application (e.g. Arduino 16.app) in the Finder, and select Get Info from the File menu. In the info panel, click the Open in 32 Bit Mode checkbox. You should then be able to launch Arduino normally.

http://arduino.cc/en/Guide/Troubleshooting#toc2