I have been in touch with Logitech and they are working on a fix for the broken accelerated scroll. In the meantime, just REVERT back to the good old 1.1.1 version. Just remember to first uninstall 1.2 using the supplied Uninstaller. And if you didn't have the foresight to backup your old 1.1.1 version (from now on, do so before you "upgrade' something... Lesson learned!), you can still download it, but not at Logitech's main web site. Logitech deletes older versions on their web site so it's no longer available. They do, however maintain an ftp site where you can download it at:

ftp://ftp.logitech.com/pub/techsupport/mouse/mac/lccinstalldisk111.dmg

Also, here is another web site that still has the 1.1.1 version for downloading posted, but you better hurry before they decide to post the 1.2 version.

http://fcg.e-node.com/logiciels_mac/000391AC-00986B8D-000391B3