Can I use the Netduino USB as a serial port?
The problem is that the Netduino uses the USB port for communicating the debugging information required so you can live debug through visual studio.

It is possible to switch the Netduino and use an FTDI serial cable to do the programming/debugging which will leave the USB port free for communications. There is a thread about this on the Netduino forums.

There are also discussions here and here that confirm they are working on the problem.