We just upgraded from 2008.2.1001 to the latest 2008.3.1314 and now the callback stopped working on the Toolbar.  
I previously had a few buttons on the toolbar that had Postback="False" and one button that postback was working on. 
I tried setting AutoPostback="true" on the toolbar and removing all of the Postback="false" settings on each button but it still doesn't work.  I even removed the ajax manager that was hooked up to it and it still doesn't postback to the server.
The OnClientButtonClicked event is still working.

Thanks.

Has anyone else run into this issue?  I guess I could create a workaround by having it execute a ClientOnClick event and then catching that button and manually executing an AJAX request, although I would rather have the control work as it did in the past.  Not sure if/why the functionality to have a button postback to the server would be removed but it sure is a pain in the butt.

Hello Iggy,

There really were some issues concerning RadToolBar's onButtonClick event which are fixed already. Please download tomorrow the latest internal build form your client.net account and give it a try.

Greetings,
Yana
the Telerik team

After running into this issue more I found out what the problem was.  For some reason when you set the CssClass property on a RadToolBarButton control, the postback stops working.  I haven't messed around with it more to see if it affects postbacks from other buttons on the same toolbar or not but just thought I would let people know what causes the issue.