Trying to make it work for user-folders, allow storing the files added to the ramdisk so I can use it for "~/Library/Caches/Google/".

MoveTemporaryFoldersToRamdisk_MacOSX.sh

#!/bin/bash

# +----------------------------------------------------------------------+
# |                                                                      |
# |  Set up Mac OS X to store temporary files in RAM rather than on disk.|
# |                                                                      |
# |  By Philipp Klaus <http://blog.philippklaus.de>                      |
# |                                                                      |
# |  Originally by Ricardo Gameiro <http://blogs.nullvision.com/?p=357>  |
# |  Changes by Daniel Jenkins                                           |
# |     <http://blogs.nullvision.com/?p=357#comment-1140>                |
# |  Changes by CW Shue                                                  |
# |     <http://blog.cwshue.com/2012/11/moving-tmp-folder-to-ram-disk.html>
# |                                                                      |
# +----------------------------------------------------------------------+

cd /Library
sudo mkdir RamFS
sudo chown -R root:wheel RamFS
sudo chmod -R u+rwX,g+rX,o+rX RamFS
cat << "EOF" | sudo tee RamFS/RamFS > /dev/null
#!/bin/sh
# Create a RAM disk with same perms as mountpoint

RAMDisk() {
    mntpt=$1
    rdsize=$(($2*1024*1024/512))
    echo "Creating RamFS for $mntpt"
    # Create the RAM disk.
    dev=`hdik -drivekey system-image=yes -nomount ram://$rdsize`
    # Successfull creation...
    if [ $? -eq 0 ] ; then
        # Create HFS on the RAM volume.
        newfs_hfs $dev
        # Store permissions from old mount point.
        eval `/usr/bin/stat -s $mntpt`
        # Mount the RAM disk to the target mount point.
        mount -t hfs -o union -o nobrowse $dev $mntpt
        # Restore permissions like they were on old volume.
        chown $st_uid:$st_gid $mntpt
        chmod $st_mode $mntpt
        # Rename the new disk to previous name
    	diskutil rename $mntpt `basename $mntpt`
    fi
}

StoreRAMDisk() {
    mntpt=$1
	tmpmntpt=/tmp/rd_mntpt
	# retreive the device path eg: /dev/disk4
	dev=`mount|grep $mntpt|awk '{print $1 }'`
	# unmount the disk from the dir, the previous files are left in the dir
	umount -f $mntpt
	
	# mount the dir to a temp dir
	# Create.. 
	mkdir $tmpmntpt
	# Mount
	mount -t hfs -o nobrowse $dev $tmpmntpt
	# Move all files to the original dir
	mv $tmpmntpt/* $mntpt 
	# (rsync seems better, but doesn't works?)
	# rsync -a --remove-source-files $tmpmntpt/ $mntpt
	# Unmount and remove the tmp mount dir
	umount $tmpmntpt
	rm -rf $tmpmntpt

	# Remove the RamDisk to free up memory
	hdiutil detach $dev
}

# Test for arguments.
if [ -z $1 ]; then
    echo "Usage: $0 [start|stop|restart] "
    exit 1
fi

# Source the common setup functions for startup scripts
test -r /etc/rc.common || exit 1 
. /etc/rc.common

StartService () {
    ConsoleMessage "Starting RamFS disks..."
    RAMDisk /private/tmp 256
    RAMDisk /var/run 64
    #RAMDisk /var/db 1024
    #mkdir -m 1777 /var/db/mds
    # RAMDisk /Users/larrybolt/RamDisk 1024 # It doesn't works for a weird reason :(
}
StopService () {
    ConsoleMessage "Stopping RamFS disks, nothing will be done here..."
    # diskutil unmount /private/tmp /private/var/run
    # diskutil unmount /private/var/run
    # StoreRAMDisk /Users/larrybolt/RamDisk
}

RestartService () {
    ConsoleMessage "Restarting RamFS disks, nothing will be done here..."
}

RunService "$1"
EOF
sudo chmod u+x,g+x,o+x RamFS/RamFS


cat << EOF | sudo tee LaunchDaemons/com.nullvision.RamFS.plist > /dev/null
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-/Apple/DTD PLIST 1.0/EN" "http:/www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>com.nullvision.RamFS</string>
    <key>ProgramArguments</key>
    <array>
      <string>/Library/RamFS/RamFS</string>
      <string>start</string>
    </array>
    <key>KeepAlive</key>
    <false/>
    <key>RunAtLoad</key>
    <true/>
    <key>UserName</key>
    <string>root</string>
    <key>StandardErrorPath</key>
    <string>/var/log/RamFS</string>
    <key>StandardOutPath</key>
    <string>/var/log/RamFS</string>
  </dict>
</plist>
EOF