If you connect an HDMI splitter to the Sky HD box output, then connect two HD TVs to it, is there any loss of quality compared to just connecting the one HD TV directly into the Sky HD box?
The longer answer is that generally you don't loose image quality (though its not impossible) but you can run into EDID and HDCP handshaking issues so don't assume all units are created equal.
If you have a long cable run to one of the Displays you may want to ensure the 1x2 DA includes some form of signal equalisation.