Guest account on Lion vs Mountain Lion When you enabled Find My Mac on Lion or ML, it creates a guest account for you.
In Lion clicking on the guest account would restart the computer into a Safari only mode.
In Mountain Lion the guest account is traditional account except the user's data is deleted when they log out.

What was the point in the Lion guest account, I heard something to do with helping to locate the Mac if you lose it, but I don't understand how having a guest account enabled and not normally in use helps? If someone finds a Mac, and happens not to steal it, how would logging into the guest account help? It seems like this is a very small use case, and not really enough to warrant having the feature, so I'm sure I'm missing something?

Why is Mountain Lion's guest account enabled when you enable iCloud/Find My Mac? What is the connection between them?

I can't see any reason to keep the guest account enabled on Mountain Lion?
The Guest account is enabled in Lion and ML for the Find my Mac feature as it enables the location function for the Find My Mac feature to work. Without the guest account, the location feature will not turn on and therefore will not work. 

Disabling the Guest account will effectively disable usage of the Find My Mac feature.