SETI doesn't use ANY cpu optimizations AFAIK. Not even SSE, nor 3DNow!.
Taken from the FAQ:
"Are you planning on optimizing the SETI@home client for the G4/3DNow/etc instruction set?
As of yet, there are no plans to optimize the SETI@home client for any particular platform or processor. Future versions of the client may be optimized, but there are no plans for doing so in the immediate future."
If my baby don't love me, I know, I know, her sister will.