OS: Xubuntu 14.04; Xfce version: 4.10; xfwm4 version: 4.11.1-2ubuntu3.01; theme: Zukitwo; icon theme: Evolvere Blue Folders Dark fallback. Download as pdf here or here.
Update, 2014-07-24: Guided by Reddit users valgrid and nsdragon, I’ve found a flaw in this tutorial. Both were unable to find titleless_maximize in their versions of Settings Editor, and adding the property manually yielded no results. After some searching, I believe I’ve found the cause to be the version of xfwm4. The current available version is 4.11.1-2ubuntu2, whereas the tested version was 4.11.1-2ubuntu3.01, which was installed from Eugene San’s PPA. This blunder on my part means that if you can’t find titleless_maximize, you may need to wait for an updated version of xfwm4 or install the patch, after all. Colour my face red.
I found a little quirk when I upgraded to Xubuntu 14.04: the titlebar no longer appeared when I maximised a window. Because I habitually exploit the titlebar, this was a cumbersome change (or bug). Fortunately, I found out how to reverse it quickly enough.
Initially, I thought the solution was obvious enough to go without a mention. A recent article by Andrew on WebUpd81, though, introduced the intriguing xfce4-windowck-plugin2 by Alessio Piccoli and Cédric Leporcq. It's a set of two plugins enabling you to place a maximised window's title in the panel, along with the window's buttons. If you install xfce4-windowck-plugin, you likely want to disable the titlebar to avoid redundancy. Andrew and xfce4-windowck-plugin's developers suggest installing the external program Maximus or a patch for xfwm43.
My solution is simpler and doesn't require you to download or install anything.