PuTTY, CygwinX, and X11 forwarding connection refused

Ok, I figured out the solution to my own problem.

By default CygwinX no longer listens for tcp connections (Cyg SSH is using Unix sockets to connect). To enable tcp connections "-listen tcp" needs to be added to the command line parameters. In my case I changed the "XWin Server" icon to read:

C:\cygwin64\bin\run.exe --quote /usr/bin/bash.exe -l -c "cd; /usr/bin/startxwin -- -multiwindow -listen tcp"