Using 13.04 and GS3.6.3? Cheers.
Windows free since '09 - never looked back!
i've not tested with GS, but with unity if you select an icon & hold down ctrl, then you can drag the icon where you want it to. Right click on the icon also have some options.
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You need to be more specific about what you mean when you say panel icons. Perhaps you could include a cropped screenshot?
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If you mean the icons for wireless, username, bluetooth, etc. (I'm not sure if this is called the system tray in GS but it's similar) then I don't think you can rearrange the order. You can specify which ones to display with gnome-tweak but not the order, as I recall. Of course the last version of GS I used was 3.4 so this may not be correct.
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Session fall back Alt-Right Click on the icon to be moved should produce "move option"
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