I tried switching the default login manager (gdm) to lxdm, but it just crashes after I enter my password.
lxdm writes a bunch of errors into /var/log/lxdm.log:
** Message: find greeter (nil)
** Message: find idle (nil)
xauth: file /var/run/lxdm/lxdm-:0.auth does not exist ** Message: add xserver watch
Invalid MIT-MAGIC-COOKIE-1 keyuse: X [:<display>] [option] <help for command line options>
I've also tried SLiM - it lets me in, but a bunch of things don't work in the xfce shell -- volume control is busted, NetworkManager seems to randomly forget the wifi passwords, and so on.