Since Linux Mint 11 (Ubuntu 11.04) new overlay scrollbars in the Gnome-Desktop are used.
If you want to get rid of them because you don't feel comfortable with it or for whatever reason it is no problem! - There are different ways to do this:...

1a) Probably the easiest way to remove them for all users is to uninstall the packages:

• open a terminal and insert
• sudo apt-get remove overlay-scrollbar liboverlay-scrollbar-0.1-0
• type in your administration password
• wait a few seconds (till the operation in the terminal is finished)
• then reboot your system and that's it!

To undo this is as easy as removing them:

• open a terminal and insert
• sudo apt-get install overlay-scrollbar liboverlay-scrollbar-0.1-0
• type in your administration password
• wait a few seconds (till the operation in the terminal is finished)
• then reboot your system and the overlay-scrollbars are back again!

1b) You can also use your graphical package-manager (in most cases synaptic) to remove the two packages overlay-scrollbar and liboverlay-scrollbar-0.1-0.

To get the overlay-scrollbars back install this two packages again.

2a) Disable the overlay-scrollbars for all users (without removing packages):

• open a terminal and insert
• echo export LIBOVERLAY_SCROLLBAR=0 | sudo tee -a /etc/X11/Xsession.d/99disable-overlay-scrollbars
• type in your administration password
• then reboot your system and the overlay-scrollbars are gone!

2b) You can also create the file /etc/X11/Xsession.d/99disable-overlay-scrollbars (if it doesn't exists) an add the line export LIBOVERLAY_SCROLLBAR=0 with your favorite text-editor. (Superuser permissions are required - be careful!)

To undo this remove the line you added to the file like in point 2b) above. (Superuser permissions are required - be careful!)

3a) Disable the overlay-scrollbars for one (the active) user:

• open a terminal and insert
• echo export LIBOVERLAY_SCROLLBAR=0 >> ~/.xprofile
• then reboot your system and the overlay-scrollbars are gone!

3b) You can also use your graphical file-manager (in most cases nautilus), show the hidden files and create the file .xprofile in your home-folder (if it doesn't exists). Then open it in your text-editor, add the line export LIBOVERLAY_SCROLLBAR=0 and save the file.

To undo this remove the line you added to the file like in point 3b) above. If it is the only line in this file you can also remove the whole file.

These methods are tested and work quite good!

Source: http://askubuntu.com/questions/34214/how-do-i-disable-overlay-scrollbars