I am using Python 2.7.3 on OS X 10.8.3, installed with MacPorts. If I hit command + c or command + x on content in IDLE, I can paste it with command + v into other apps. However, I cannot use command + v to paste into IDLE itself, either from other apps or from within IDLE.
If I highlight content in IDLE, a right-click on the mouse will duplicate (i.e. paste) that content. This is sort of a workaround, but it is annoying not to be able to paste URL's or code from outside of IDLE.
Make sure that you have the cursor more than one space after the last >>>
. It won't paste unless you do.