2 Site Exchange 2010 CAS Array - Active/Active with GTM

It's very similar - but I am obviously advocating APM approach. :)

 

 

 

APM provides scalability(APM can process up to 600 logons/sec and up to 60,000 concurrent users depending on the platform), performance(you benefit from a single SSL offload and do not need to re-encrypt to TMG), single point of management, and since APM is just a module, you can turn it on on and not worry about provisioning and managing TMG instances to do this.