I posted half a dozen links in 3TB thread on PowerMac G5 taken from WD support and elsewhere, including Apple docs on support and the reasons behind GPT to support larger drives (as well as how it is needed for EFI based systems).
Intel may bring out more support for EFI with next generation of chips and the motherboards to support new socket, as well as the need to some extent to have support for booting Windows 64-bit and future on 2.5TB drives.
Hitachi 7K3000 3TB
http://macperformanceguide.com/Storage-Drive-Hitachi-7K3000-3TB.html
Apple Secrets of GPT TN2166
http://developer.apple.com/library/mac/#technotes/tn2006/tn2166.html
http://www.wdc.com/en/products/products.aspx?id=120
There are some mentions of Mac OS X 10.4.6 or later for support of very large volumes.
Mac OS version 10.4 onwards (Tiger, Leopard and Snow Leopard) can use the GUID Partitioning Table scheme (GPT) which will align an Advanced Format drive correctly.
Mac OS versions using Apple Partition Manager (APM) will not align partitions correctly and will not provide optimum performance.
Advanced Format