Script Summary: This Greasemonkey script will remove ALL Facebbok activities, one "page" at a time.
Made a small change to support the new Facebook profiles.
Load it up in Greasemonkey and go to your Facebook Profile Page.
Press Ctrl + F5 to reload your Profile Page if the button does not show up above your activities.
To delete more activities with one click of the button, scroll down until autoloading of older posts stop, then click the link "Older posts" which should magically appear.