misschievous,
when i use Fix + i notice my frost or metallic e/s are more metallicy or frosty and colors come out. matte and other less shimmery finishes stand out. over all, it really adds a lot of glow to your skin and the benefits are pretty great. i think it just makes makeup look more tailored and finished. try it out at a mac store before you buy it though. i know a girl who had a weird puffy reaction to it-- so it isnt for everyone.
i was skeptical about the hype before i tried it. if you are interested i have pics of foundation buffed without it and then with it. PM me if you want me to post them, or email them to you.