So I got my retail copy of SL today... And Ive tried installing it twice, Both times the install failed, like with 1 centimeter away from being finished... Here is exactly what it says:

Mac OS X could not be installed on your computer

[caution sign]

The installer could not start up the computer from the disk "MAC OS". Try selecting your disk using the Startup Disk utility.

Click Restart to restart your computer and try installing again."

So yeah...