This seems to affect some people more than others, and I have read the same complaint on the forums of other distros so it's not unique to Salix.
I found the fonts on the XFCE version to be unclear too, but they are much improved after recompiling freetype with subpixel rendering enabled, as discussed on Dugan Chen's site:
http://duganchen.ca/writings/slackware/fonts
I also used the Lagm LCD test which he recommends (
http://www.lagom.nl/lcd-test/subpixel.php) to find my monitor's subpixel layout and set this in XFCE's settings - not sure how you would do this in Fluxbox.
Interestingly, not all applications are improved after these changes. Most are much better though, including XFCE menus, dialogues etc, as well as font rendering in Thunderbird and Firefox. My preferred browser, Chrome, is still a little fuzzy, as are the fonts of certain applications such as VirtualBox. There are obviously lots of factors at play here...
Andy
P.S. There are a couple of threads on this topic in the forum already and I found the link to Dugan's site in one of them.