Edit: Unfortunately, the images originally included in this post are gone, because of hosting problems in late 2009. My apologies.
I had a little free time today, so I split my efforts and tried two different approaches on two of my favorite distros, on two different machines.
It took a little effort to get it set up, but once it was working it was quite enjoyable. LXDE was a rather random collection of pieces for a long time, but it’s starting to come together quite nicely. The panel is improved quite a bit, and the file manager is making leaps and bounds. It’s a joy to watch.
It works very well with an Ubuntu system too, with deb files for pretty much everything. If you do decide to follow the installation instructions, I’d suggest copying both mirrors into your sources.list file — both the Ubuntu and Debian lines. Some packages seemed out of date or missing from one repository or the other, but enabling both seemed to cover all the gaps. And if you need a newer PCManFM than the one that’s in the Hardy repos, check getdeb.net. It’s probably not the absolute-newest build, but it satisfies the version requirement.
Speedwise I think LXDE does a good job keeping the basic Ubuntu environment from becoming too heavy, while putting a lot of practical — and aesthetic — controls at your fingertips. Keep watching this: It’s going to get very good, very soon. :)
The second machine, the slower Thinkpad, got a fresh Arch installation, this time with pure Gnome as the desktop environment. This was mostly an experiment, as suggested elsewhere, to see how the Arch Gnome compares to the Debian Etch version.
Startup for the Arch version comes in about 20 seconds sooner than its Debian cousin, and performance seems a little snappier, but otherwise it’s hard to distinguish between the two. Of course, Debian comes with a lot of preinstalled software that you otherwise have to select and configure in Arch, and setting up an Arch system takes a little more effort (but less time, really) than a Debian system.
Arch’s trump card is probably that all the software is considerably newer than Etch. It’s true, you get more in Debian, but everything is quite out of date. You could try the freshest version, but I can’t promise you you’ll get anything that’s even near where the Arch packages stand. (And as I discovered, the sluggishness that plagues Ubuntu Gnome is evident in the newest versions of Debian Gnome. It’s sad but true.)
All the same, I’d have to call them more or less even. What you don’t get in one, you definitely get in the other, so it’s up to you which side is more important. For my own part, I’ll probably stick with Arch, just because I prefer things like pacman over aptitude, and so forth. You can decide for yourself. :)