SSE support is software-specific - either you have programs that have been recompiled to use it, or not. Adoption is pretty limited so far, between being a very new feature, and not being supported by AMD.
There are some other technical advantages to the 9000 series - some other IPC improvements, and lower power consumption due to being 45nm. Whether any of this is worth it to you depends on your budget 🙂 The overall speed differences are not what you'd call "impressive." It's just a refresh.