Reason song files are totally compatible between MAC and PC.
Here's what you need to keep in mind when using Reason on multiple computers, no matter what OS you are running:
Reason references patches/samples etc by their folder structure location, so all computers should have the same folder structure or Reason will ask you to manually locate patches/samples it cannot find.
This can be easily overcome by using the "self contain" feature - or by creating a project folder, putting all files related to the project in that folder, then using zip/rar to share the whole folder.
if you use ReFills, you will both need the ReFill.
if you use Rack Extensions, you will both need the Rack Extensions - it is possible for one person to own the RE and the other to use it via a trial.
HP Pavillion DV7T-3300 Laptop | i7 Q720 @ 1.6 GHz | 4GB RAM | Win7 Pro 64-bit
m-audio Axiom Pro 61 keyboard controller || iPad2 | RetouchControl DUO | TouchOSC | LoopBe30 MIDI
m-audio Mobile Pre USB (original) audio interface | ASIO4ALL || RØDE NT-3 mic
Reason 6.5.3 || Pulsar | Saturation Knob | Rough Rider | TSAR-1 | Uhbik-A | Re-Tron | Polar | Echobode | Uhbik Q | Uhbik F | Morfin XF | Uhbik S | Uhbik D | Uhbik G | CV Suite Line Processor | wbl5515 | Uhbik P | RE-2A | Radical Piano