Apparently, the LXDE version is supposed to be for older computers, the Xfce version for users seeking an alternative to GNOME 3 and Unity, and the Enlightenment version for adventurous users.
Aptosid is another lightweight distro released last week. It's based on Debian unstable and features the KDE and Xfce desktops.
Finally, PagugLinux 11.1, a "minimalist, Gentoo-based live CD featuring the Fluxbox window manager," was released.
DistroWatch Weekly, Issue 414, 18 July 2011