I was having problems writing to my Arduino Mega (1280) with Arduino 1.0.5 on a clean install of OSX 10.9 Mavericks.
[u]Symptom[/u] When programming, I get the error: avrdude: stk500_recv(): programmer is not responding
[u]Diagnoses[/u] According to http://www.enttec.com/support-center/kb/article/108-OS_X_Mavericks_(10.9)_-_IMPORTANT Apple has developed their own FTDI drivers for OSX 10.9. These drivers are problematic.
[u]Solution[/u] (as partially provided by the website above) Type the following commands into the terminal: cd /System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns sudo mv AppleUSBFTDI.kext AppleUSBFTDI.disabled sudo touch /System/Library/Extensions
Restart your computer
Install the original FTDI Virtual Com Port drivers found here: http://www.ftdichip.com/Drivers/VCP.htm
Start Arduino and program as you always have.
[u]Disclaimer[/u] This solution solved my problem. If you are having problems since upgrading to OSX 10.9 Mavericks, there is a chance this will be your problem too. If this does not work, I can't help you out. If someone knows a simpler way to do this, please let me know. If this is documented somewhere and I missed it, please let me know.