Author: Jonas Bilinkevicius 

Is it possible to detect when the Windows taskbar's position has been changed 
(moved or resized)? I'm sure you could just hook it and grab its messages 
(ABM_...), but is there a less involved way?

Answer:

The taskbar broadcasts a WM_SETTINGCHANGE message when it changes size or position.

private
1   
2   procedure WMSettingChange(var msg: TWMSettingChange); message WM_SETTINGCHANGE;
3   
4   procedure TForm1.WMSettingChange(var msg: TWMSettingChange);
5   var
6     r: TRect;
7   begin
8     if msg.Section <> nil then
9       if StrIComp(msg.section, 'windows') = 0 then
10      begin
11        SystemParametersInfo(SPI_GETWORKAREA, 0, @r, 0);
12        memo1.lines.add(format('Workarea is %d, %d:%d, %d', [r.left, r.top, r.right,
13          r.bottom]));
14      end;
15  end;