You can have the taskbar buttons 1-2 pixel apart if you want in Windowblinds Dave.
Well you made me look. Keep in mind that (I think) he's wanting to actually compact the buttons.
Image Below - The top 7 WB skins are from different skinners over a period of time (one is Aero Midnight). Hopefully it's a decently random sample with various settings. The bottom two are a curtains skin, before and after trimming the extra transparency off the edges.
After eliminating the Start Buttons which do vary, the button objects themselves all take up the same spaces and land in exactly the same places, everything else is just visual. That was an interesting masochistic exercise, next perhaps I'll try to untangle the wires under my desk.