I haven't had any luck. Have been able to get a number of other things happening in 2.4 but not widgets (other than those that come with the blog module. Is there any reason that these should work and not others?)
So, since you have the widget tab appearing you must have the code in page.php in place. Thats the same point i have got to.
I am testing the page-elements module (the trunk works with 2.4 details can be found on the developers site). It gives me the ability to have multiple sidebars (or any other holder) and load 'elements' into each. An element is much like a widget, a few are supplied and you can create more if you need...
Anyway... until I get widgets workin I am happy with this solution.