I had this question as well. After sniffing around, it looks like the magmi-0.8 folder may be reserved for the future releases of Magmi 0.8. The current stable is 0.7.19
I tried to run the magmi-0.8 version but got a bunch of errors, so I am now running the app from the base magmi folder. Fingers crossed this version plays nicely with Magento CE 1.8
This post provides more info: https://github.com/dweeves/magmi-git/issues/12