Sideloading Apps on Google-TV
Unfortunately the ADBD (adb daemon) is not enabled on any current Google TV hardware, so adb connectivity is not possible via USB, Ethernet, or any other means.

However, a few crafty tinkerers from GTVhacker site managed to hack the Logitech Revue unit to enable this functionality.  Keep in mind that this is a hardware hack and includes physically opening up the Revue box and soldering connections on the motherboard.  You can read more on this mod here.  Needless to say, this hack is not for everyone, and carries even more risk of bricking the STB as a plain software hack.