I thought I would share this with the community as I have had this issue now for ages and I have tried everything to fix it.

I have had my hackintosh up and running several times and then out of nowhere, this laggy dock problem would occur. This was only one of the symptoms with the full list of symptoms being: magnification problem with dock, very slow genie effect when minimising window, jittery performance when using menus, issues within any running program because of all of these.

I thought it was an issue with my 9400 GPU and went through numerous steps mentioned in forums to try and fix. Deleting/replacing kexts, altering GPU IDs, changing BIOS settings. I even reinstalled snow leopard to remedy the problem (until it happened again).

The problem and solution - it seems my logitech wireless mouse was the issue. I unplugged it and plugged in a standard non wireless mouse. Bingo no more issues!
I don't have a clue why this could be but if you have any of the aforementioned symptoms try this solution first!!