The HCTS 4.2 release includes new features such as support for hard drives with more than one terabyte capacity. Lots of good info here: Updated FAQ, Getting Started Guide, Release Notes, README, and more.
The HCTS program enables independent hardware vendors (IHVs), system manufacturers, system integrators, and end users to certify their systems and components for the Solaris OS and OpenSolaris. All hardware that passes certification testing is eligible to be included in the Solaris OS Hardware Compatibility List (HCL). Certification tests for x86 and x64 products cover both 32-bit and 64-bit architectures.