I just installed the amd64 version of Debian Lenny (v5 beta 2). It looks very promising. It comes with kernel 2.6.25.2 and is very up to date. Exim, kernel and most of the packages are newer that Ubuntu 8.0.4.1.
The install was very smooth and I encounted no problems at all.
I have settled on Ubuntu 8.01.1 as a desktop. I have modified it and run the desktop as a superuser to avoid the sudo thing. It is very stable (I use the AMD 64 version) and all the multimedia plugins work well. I recently installed Flash 10 and nspluginwrapper 1.0.0. I had to compile nspluginwrapper to upgrade to version 1.0.0 (probably not necessary).
To install flash 10 it was necessary to install getlibs from http://www.boundlesssupremacy.com/Ca…etlibs-all.deb and the following libraries to get it to work correctly with nspluginwrapper:libnss3-1d, libnspr4-0d, libcurl3.