Not that much!
Actually, i think this problem is much worse when using small icons. The space around it actually takes almost the same amount of space of the icon itself (so doubling the needed space).
A regedit fix for this would be excelent, but I hadn't had any luck so far.
I too feel that the icon spacing in the taskbar (64 bit Windows 7) is too far apart. I understand that the taskbar design serves a dual purpose - quick launch and 'open' apps. However it looks very odd and there should be a way to squeeze them closer together.
1.Right click on the taskbar
2.Select : Toolbars--->"New Toolbar"
3.Enter this line in the folder line : %SystemDrive%\Users\%username%\AppData\Roaming\Microsoft\Internet Explorer\Quick Launch
4.Make sure the right folder appeared on the list, then press "Select Folder"
5.Unlock the taskbar
Voila! Seems like you got the good ol' quick launch bar
First; remove all your win7 default quick launch icons one by one with right clicking on them and "remove from taskbar" or such...Than, right click on ur good ol' quick launch bar and uncheck the rows which are "show text" and "show title", now you should have the icons only, like the old way. (btw make sure you selected "small icons" during the process, or keep it big if you like it so, i'd guess you like it small due to your spacing obsession)
Now is the frustrating part...You can do it at the first time or 10., but all you need to do is now hold the "left seperator" with holding left click and lean/push the seperator to the start button and cause it make a jump and switch side up to the next to right bottom icons. If you manage to do that, hold the right seperator and push the icons to the start button, than lock the taskbar...Woosh...What an effort... (My friend told me that he adjusted the seperators the other way around, and managed to achieve the same look so try all the way around till you get the exact old quick launch look, good luck)