In xsettings /Xft/Lcdfilter isn't applied if set with xfconf-query, neither as string or int.
I've added this in 4.9.0, in 4.8 this is disabled.
We're not going to fix this in 4.8 and this should work in 4.9. To check this you can run xfsettingsd with XFSETTINGSD_DEBUG=1 exported.
Just wanted to note that the reason for opening this bug is that I was hoping to get the filtering option into the fonts dialog of XFCE (preferably on by default), and while at it, was trying to enable it via xconf-query, and it didn't work. As I told Silvio on IRC, after extensive tests and comparisons, I believe the only thing which makes Ubuntu fonts rendering so wildly acclaimed is actually only the LCD filter turned on. The relevant patches that improve the filter landed on upstream xorg not too long ago, and are already available at debian sid, and possibly other distros. For reference, few sample renders taken on relatively clean aptosid (debian sid), with droid-sans and ubuntu fonts: Without lcd filter: http://i42.tinypic.com/1hf612.jpg With lcd filter:http://i40.tinypic.com/aop0s7.png Top: Ubuntu 11.10 (inside virtualbox) at default rendering, bottom: my box with lcd filter turned on (the right side zooms are respectively of the left side texts): http://i44.tinypic.com/ws8sxw.png This should really be turned on by default...