I have installed skype on my fresh squeeze 64bit system. It works fine except for the fact that the gtk theme isn't really working and the result is quite ugly:
How can I fix this?
Skype is a proprietary 32-bit application, and cannot use 64-bit Gtk+ theme engines.
Try installing ia32-libs-gtk, which provides several engines. If that doesn't work, you'll have to change themes so that you are using an engine which is available in 32-bit.
You can put this in your ~/.bashrc so it is always available.
Also, try this:
ephemient's idea is intriguing. Try installing other GTK engines and switching to them to see whether Skype is able to use the new ones without falling back to Raleigh. I know it sounds nightmarish, but you can also run Skype under strace and see what files it fails to open (if any). Also, what engine are you using? Gnome/GTK 2 or 3?
As another data point, I'm running it under Ubuntu 11.10 64-bit with Unity and Radiosity and it picks up the engine correctly.
A final note: I would comment on epemient's answer, but I suffer from low karma here. :-(