Steps to reproduce:
1- Launch Blender. The default file's camera/light/cube is enough.
2- switch to a node editor. Enable Use Nodes (compositing nodes)
3- Hit render
4- Hit ESC to return to the node editor.
5- select all the nodes.
6- press the copy (Ctrl-C ) button in the node editor header.

result:
Segfault after a short pause.

OS:
GNU/Linux (Fedora 17) 64 bit, Intel Quad CPU, Nvidia GPU.

Note:
Unchecking Use Nodes, saving the file, restarting and opening the file allows one to copy/paste, so long as you don't hit use nodes.