I downloaded the latest Fluxbuntu over the weekend and gave it a very quick spin. Here are some very hasty first impressions.
The worst news is that I could not get this "Gutsy Gibbon" Fluxbuntu release candidate to install on my old laptop. I haven't been able to get the "Gutsy Gibbon" release of Xubuntu to install on that laptop either. In both cases the problem is the same: the installer (after booting from the CD and prompting me for a bunch of info) cannot find a valid CD drive when it comes to doing the actual install work. I guess this is a typical example of Linux's hardware temperamentalness. The weird thing is that I have no problem installing older versions of Xubuntu on the same machine. Gnarly.
Anyhoo, I instead installed Fluxbuntu using Qemu (via Qemu Manager) on my workhorse laptop (1.7 GHz Intel Centrino with 1.5 GB RAM). The emulation was set up to use 128MB RAM, so this should give a reasonable idea of what would happen in a slim system. Doing some very rough benchmarking suggests that the effective clock rate of this setup is around 800 MHz. If I turn off all acceleration, then it drops down to something like 300 MHz.
Anyhoo, anyhoo, the installation went fairly smoothly--except for it asking me to install native language files for an English language install. Now for the report card.
First, the worst part. Startup is slower than expected. A lot slower. Like, "Is it working?" slower. But in the end it does start up. I wasn't able to tell what DM they are using yet, but it has been Fluxbuntu branded and it looks pretty nice. Still, the slowness may be due to a DM that's more bloated than it really needs to be. Or it may be because there's a lot of daemons, etc. starting up. The weird thing is that Xubuntu doesn't take as long to get going.
Once inside, you are presented with a very attractive desktop. I noticed some sluggishness, so I disabled the soothing wallpaper in favor of a solid backdrop. That seemed to help a bit.
I set up the emulated screen with 800x600 resolution, and sure enough one of the problems that I have seen with a lot of distributions manifested itself here as well: DPI ambiguity. Almost all 800x600 screens are physically 75 dots-per-inch screens, but they are treated as 100 DPI by some applications in many Linux installations. I solved this problem on the system(s) I have been developing by adding explicit DPI configuration information to the files that affect X-server startup (I am using XDM). This seems to solve the problem for all but the oldest or worst designed programs. In theory this should be possible with whatever DM Fluxbuntu uses as well, but it require some more research to find out 1. what DM they are using and 2. how to change the config stuff. (In fact, given the slow startup that I have already mentioned, it may make sense to just replace it with XDM because it is leaner than anything else I know.)
I found it interesting that the Fluxbuntu people opted to use ROX-filer for file management and managing desktop icons; they are also using Leafpad as the default text editor and settled on Abiword and GnuMeric. It's interesting because I have settled on exactly the same applications for the same, er, applications.
However, for web browsing Fluxbuntu uses Kazehakase rather than Firefox or Iceweasel. I will need to use it a bunch more to see what it's like. Fluxbuntu uses a similarly obscure email client, Claws, rather than the now-classic Thunderbird.
One thing that I will need to test is what happens to the non Debian-menu menu items in the Fluxbox menu after installing new apps.
My impression so far is that Fluxbuntu looks promising, but it will need some tweaking if it's going to work on PII-era machines.