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There's no guarantee until it comes out, but based on Lion, you should be able to. Most of the time it updated itself via the AppStore, however there were a few builds that did it via Software Updates.
 
And what about the first installation of 10.8 over Lion?

I have downloaded the installer but it is still "sitting" in my application folder waiting ... One question though about installation process... is there an option to upgrade from 10.7 or a clean installation over Lion is the only way possible?

I'm shivering to the thought of having to reinstall ALL my applications, and passwords, and preferences ...
 
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