I'm slowly coming out from under something very like bronchitis, but I wanted to get this item posted because I see nothing about it online: When Mac Slow's excellent Cairo Clock is installed under Ubuntu with all the desktop defaults, it does not overlay itself on the background correctly. (See screen shot at left.) This was initially a head scratcher for me, because the very same version of Cairo Clock (0.3.4) works perfectly under Ubuntu 10.4.
What I didn't realize is that in the process of tweaking Lucid Lynx this spring (before I installed Cairo Clock) I changed the Visual Effects option from None to Normal. The clock requires something in the GNOME desktop visual effects mechanism, and when I changed Visual Effects to Normal instead of None, it worked as expected, clipping to the clock face with a nice transparent drop shadow.
The option is in the System | Preferences | Appearance dialog, under the Visual Effects tab.
Nothing more than that, and not a big deal. I'm posting it in case some other Ubuntu noob has the same problem and can't figure it out. If I can save some poor guy an hour and some hair this easily, I will.