With the upcoming Phenom II X6 processors AMD will introduce Turbo CORE, a technology somewhat similar to Intel's Turbo Boost technology. AnandTech received some details and describes how this technology works. Basically, when three or more cores are idle the frequency of those three cores is kicked back to 800MHz, the voltage to the entire chip is increased, and the remaining three cores are overclocked by as much as 500MHz. It's not as elegant as Intel's solution, but it's better than nothing.
With the Thuban cores AMD is introducing its version of Intel’s Turbo Boost technology called Turbo Core. AMD has yet to implement power gating on its processors, so Turbo Core works a little differently than Intel’s Turbo.
Turbo Core kicks in when 3 or more cores (on a 6-core part) are idle. When this happens, the frequency of those three cores is reduced to 800MHz, the voltage to the entire chip is increased, and the remaining three cores are turboed up by as much as 500MHz. It doesn’t get any more granular than this. If you have 3 or more cores idle, then the remaining turbo up. In any other situation the CPU runs at its normal clocks.