After messing around with custom kernels today on my Ubuntu installation I noticed that Cairo-dock was no longer transparent and that there was a black background underneath it as I mouse-over the dock.
It turns out that this is due to compiz effects not being enabled in Ubuntu.
To enable compiz:
Right Click on Desktop –> Change Desktop Background –> Visual Effects –> Check the Extra Box
You should now have the transparency back again.
Thank you so much for your input. It resolved the same problem I was having. It looks so much better now. Do you have any idea why my desktop effects reset themselves? I can not think of any reasons. Except that when I installed Cairo-Dock it may have altered my desktop preferences.
No problems – upgrading to Jaunty (Ubuntu 9.04) should also fix the problem and the Nvidia drivers included are fully supported as opposed to being a beta version. I might also recommend you take a look at gnome-do which is actually far superior as a dock than cairo-dock (in my opinion anyway) and the development is very active. Your desktop effects will reset themselves when you install new graphics drivers – I guess this is the cause of your problem.