In both 3.3 branch and trunk "echo stat|nc localhost 2181" fails against the ZK server on Ubuntu Lucid Lynx.
I noticed this after upgrading to lucid lynx - which is now shipping openbsd nc as the default:
OpenBSD netcat (Debian patchlevel 1.89-3ubuntu2)
vs nc traditional
which works fine. Not sure if this is a bug in us or nc.openbsd, but it's currently not working for me. Ugh.