After upgrading to 10.04 I immediately noticed that my fonts were too small. A quick look at xdpyinfo reveals that the display DPI has been set to 96:

$ xdpyinfo | grep resolution
  resolution:    96x96 dots per inch
That's not right. My Acer 3810T laptop has a DPI of 118x112 (for a 1366x768 display). But was that set by hand somewhere or was it detected incorrectly?

$ grep "DPI set to" /var/log/Xorg.0.log
(==) intel(0): DPI set to (96, 96)
It appears that it was detected incorrectly. Looking this info up we have a bug in the X server itself:

Here's the fix I've implemented:

sudo echo "xrandr --fbmm 294x166 || true" >> /etc/kde4/kdm/Xsetup
So that should suffice until the guys fix the upstream bug. If you use GDM instead of KDM you'll need to put that xrandr command somewhere else (I forget right now).