The Preempt patch has made it into 2.5
Source: Bit Keeper
Robert Love's now-famous preempt Linux Kernel patch has finally been integrated into the main tree. Quoth rml: "I removed all the sched.h dependencies and this reduced the size of the patch greatly. I now use current_thread_info() and none of the header or include hackery from before. I've tested this with and withot preemption enabled with success.