As for that three lines on the top right hand corner, its the Notification Center. Just go to the System Preferences to customize it. Again its pretty much useless for me.
Growl is one of my favorite apps. Its great to get notifications from other programs without intruding my work.
Try and see if you like it.
If still you don't like it, then you can uninstall it. Here is the guide : Growl - Removing Growl
And I just realized another cool feature Apple removed. On Mountain Lion the menu bar only shows the battery percentage remaining. On Lion it used to show both - time and % remaining.
And I read that its not coming back

>> Mountain Lion is coming, what should you know that you don’t yet know?
All in all Mountain Lion is a big let down for me.