It currently connects to HDMI TV's only, but majority of TV's are pre-HDMI, with 'Composite' the most common connection.

The ARM-A9/Tegra2 used in 'Box' supports SD analog 'Composite' TV's, and so should cost only a few $s to implement. Other new Media-Streamers still support Composite connections using the 3 RCA Yellow, Red, White sockets. The prototype provides the Audio part via the Red & White, but NOT the Yellow for Video !!!

External adapters are messy and expensive to convert HDMI to composite, so suggest use the features provided by the chipset and add the RCA Yellow connector to give SD Composite video. The product will then appeal to a greater audience in its initial year as many do not want to be forced into upgrading their TVs to HDMI just for a media-streamer.

When turn off by remote control, does the machine completely shut down power to the USB external HDD?

Corrections; the "Boxee Box" is not manufactured by Boxee but by D-Link by license, and D-Link does not have an exclusive deal with Boxee so other manufacturers can also get a license from Boxee to make Boxee boxes, this is even outlined on the wikipedia article for Boxee.

The chipset it uses is not yet publicly confirmed but said to be Nvidia Tegra 2, Nvidia's second generation ARM architecture system-on-a-chip series, so it is not the old Tegra 650 but a newer one.