Generally you can get away with 1 thermostat controlling multiple enclosures but you need to be sure that they are set up exactly the same heat wise including basking lights and heating elements. Using light globes is ok but if a globe blows in the enclosure with the thermostat the other will overheat.
My preference is for heat tape which I have never heard of failing.
As an example with this enclosure:
http://www.herpshop.com.au/widenl.jpg there are probe thermostats only in the left hand unit. The right hand unit runs as a slave.
Things to watch out for are heat sources that might effect one enclosure differently to another such as sunlight from a window or proximity to a heat source. Heat from lower enclosures will be transferred to those above. Also things like ballasts and transformers also give off heat. In the enclosure above each of the lights has a transformer in the base the heat from which will rise up through the enclosures.
Always check the temperature of enclosures with a thermometer.
Do not rely on the markings on the thermostat they are at best only a guide. (The digital thermometers on special at the Herp Shop this month are ideal -
http://www.herpshop.com.au)
As an aside all of my enclosures now have as their primary heat source heat tape under ceramic tiles. I put together a small web page showing how I have been doing this at
http://www.herptrader.com.au/TiledEnclosure