adb devices was working fine last year, but after upgrades and new software installs,
adb devices
no longer recognizes USB attached Android devices.
Her
The last time I updated my tablet, it turned off "allow USB debugging", and I spent a half hour or so spinning my wheels. Double check that that is turned on in settings.
Make sure that USB Debugging is enabled in Settings -> Application -> Developemnt, and also that the selected USB method is PTP and not MTP (not supported in OSX).
Try restarting the Mac in "Safe Mode". It worked for me (macos X.9.5)
Following the google bug submission... I set usb mode to Charge Only, and it detected the phone immediately. Pretty silly.
After connecting the device and enabling the USB debugging please go to the path of adb, which is now inside the android-sdk-->platform-tools and type the following command ./adb devices. I think this will list the devices connected.
I too am having this problem. However, it isn't just a problem with ADB, it's a problem with android devices in general on Mac OSX 10.6.6 Snow Leopard. Devices that used to work in 10.6.4 will no longer even mount the device as a USB drive. Googling to see if I can find the answers.