Excerpts from Jacek Generowicz's message of Sun Jan 15 01:01:17 -0700 2012:
When I log in and xmonad starts up for the first time, toggle struts avoids the xmobar and dzen exactly as expected. After an XMonad restart, the newly spawned xmobars and dzens stay on top of any other windows, so when MXonad is not in avoid struts mode, the status bars cover up the top/bottom of the managed windows.
This sounds like the dzen and xmobar aren't lowering themselves when they restart. I thought that was default in xmobar, but you can explicitly add `lowerOnStart=True' to xmobarrc to tell it to do so. With dzen2 IIRC it uses -e 'onstart=lower' to do the same thing. Note that this disables all the other dzen event handlers so they have to be re-added. Only applies if you use things like mouse-over to open the slave window, but most xmonad users don't use such things. There's a full list on: http://dzen.geekmode.org/dwiki/doku.php?id=dzen:option-e Regards, wmw