0.3.10 has tcatm's 4-way SSE2 as an option switch.
Use the switch "-4way" to turn it on. Without the switch you get Crypto++ ASM SHA-256.
I could only get this working with Linux.
Get 0.3.10 from http://bitcointalk.org/index.php?topic=827.0
Please report back your CPU and results! I think it's pretty clear that Core 2 and lower are slower, i5 faster. I don't think we've heard any i7 results yet. We need to know about the different models of AMD or other less common CPUs.