I went the route of having a single apple tv modulated as a channel on all the tvs throughout the home. The reason I did this was to use the apple tv as a primary jukebox for my whole house audio system with the ability to view the gui in each room (besides using the interface on my iphone) for changing songs, video etc... I was also fine with only having one source playing because it allows me to travel between rooms (living room and kitchen as an example) without having to pause whatever I am watching, I already had a similar setup with my replay tv dvr modulated throughout the house. I feel that this system meets my current needs and also is usable/understandable by the wife which is often a big factor in whatever i setup.
For this setup I chose to use the component out which i converted to composite using this product (
http://www.svideo.com/appletv2tv.html) to work with the standard video modulators on the market. I have this modulator that works great, picked it up used on ebay for $30,
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=182-720
You could certainly use hdmi with a splitter but I was less concerned with the video quality being distributed and more concerned about not having to run hdmi throughout the house and also wanted it to be a channel instead of an input. Additionally if I want the high quality video on the living room tv I just change it over to using a loose hdmi I have in that room disabling the modulation when in this setup.
Control comes through the ir repeater on the homes whole house audio system (breathaudio 2 input 4 zone system), and I also have a terk leakfrog ir repeater in the basement because it is not a zone of the system, all work great.
Again this setup has different positives and negatives but just wanted to discuss another setup method.
Merry Christmas