We haven't heard anything official from Intel just yet, but according to news and rumor site Fudzilla, the world's largest chip maker plans to limit hyperthreading support in Sandy Bridge to the Core i7 series.
All Core i7 2000 series processors will show eight threads in Windows Task Manager, while Core i5 chips will have this feature disabled. The same holds true for Intel's dual-core Core i3 CPUs - unlike current Core i3 parts, those based on Sandy Bridge will not support Hyperthreading. In addition, Core i3 parts will continue to come stripped of Turbo support.
So why the sudden change in Intel's Hyperthreading strategy? According to Fudzilla, the chip maker wants to better separate its Core ix branding in terms of performance and features.