I found this whole thing quite frustrating too. I have used magic prefs for some time, and it seems that under OSX Lion, they have actually removed the system wide forward and back buttons, however: ⌘+[ and ⌘+] will do forward and back respectively in my experience pretty much system wide.
I set the following:
OSX: Disable all the shiny new features:
Magic Prefs: bind the gestures so that two finger swipe is the keyboard shortcut, and if you set it to three finger swipe to switch spaces it does the whole left right iOS style thing they have done with Lion.
This is tried and tested working for me this morning, and i can actually carry on with my work now. - Good luck, i am sure it will work for you too.
( ps. magic prefs is a free preference pane app which is available from a google search i would post the link, but im all out of my allowed hyperlinks for this post!)