Somebody over at G.Skill must be going a little crazy - they have just started shipping not only 8GB but also 16GB DDR2 memory kits.
The 8GB kit includes two 4GB DDR2-800 modules and the 16GB kit includes four 4GB DDR2-800 modules. The RAM works at 1.8 volts on a 6 layer PCB at timings of 5-5-5-15 and are designed for Intel P35, X38 and X48 based Intel motherboards.
These modules are clearly stated to be for desktop users and do not include ECC support which is a must for servers. I have never heard anybody tell me they want 8GB let alone 16GB - show me a program that a regular user is using that can actually take full advantage of 8GB and 16GB.
If you have a 64-bit operating system and loads of cash to blow, consider it. If you don't, then do yourself a favor and save your money. More details at the product website.