I really don't know how to solve this on my own so I thought giving this site a chance. After upgrading to Lucid I ran into some problems. With some experimenting I came to a conclusion that if I enable subpixel smoothing on fonts the moment I start any other application not native to GTK+ (wine, openoffice, wxWidgets, ...) my X server crashes the same moment.
At first this seemed like something went wrong during installation. To cut the long story short, after 3 clean installations and whole bunch of experimenting the same thing happens all over again. Strange thing is... if I configure any other font smoothing besides subpixel, everything works like it should.