A new sample was posted recently by Joel Pobar (a Program Manager in the CLR team)

C# command line FTP server
A lightweight implementation of the FTP RFC spec. Supports the following: Supports most of the common FTP commands that FTP clients like CuteFTP and LeechFTP support. Upload and download files Delete files Restrict a user to their home directory and further subdirectories. Late bind to a logging assembly (create your own logging infrastructure) It has not been tested from a security standpoint. It’s just a reference implementation. Enjoy!