Here is my setup for mounting various elements of the system. With this, I have managed to reduce the overall usage of the RAM, and KDE works better.
/etc/fstab:
rootfs          /               auto      defaults,noatime          1  1
proc            /proc           proc      defaults                  0  0
devpts          /dev/pts        devpts    mode=0620,gid=5           0  0
usbfs           /proc/bus/usb   usbfs     defaults                  0  0
tmpfs           /var/volatile   tmpfs     defaults,size=1%          0  0
tmpfs           /run/shm        tmpfs     mode=0777                 0  0
/dev/mmcblk1p2  swap            swap      defaults                  0  0
/dev/mmcblk0p2  swap            swap      defaults                  0  0
By default, I have swap partitions on both SD cards, so that I can always have swap, regardless of how many SD cards I have in pandora - see the swapon/swapoff utils for details on managing swap.
/etc/default/tmpfs:
RAMLOCK=no
RAMSHM=no
TMPFS_SIZE=1%VM
RUN_SIZE=1%
LOCK_SIZE=26214400 # 2.5MiB
SHM_SIZE=1%
TMP_SIZE=1%
I have 1GHz pandora with 512 MB RAM, and with this setup, I have managed to keep the RAM usage to around 300-400 MB and that is while running KDE, postgresql, apache, and several firefox and terminal windows, and development instance of django. So far, I haven't seen more than 50 - 100 MB of swap usage. I have copied the scripts from pandora that do the setup, because I still haven't had time to check all of them and clean them from the stuff I don't need, but I have disabled zram because I don't need it.
System is very responsive and usable. And of course, the parameters depend on what you do.
I'm using KDE because I'm toying with KDE and python, but I guess that for XFCE and some other lightweight X managers the RAM usage would be even less.