Customizing Ubuntu to run from RAM only, within GRUB options

I'm interested in exactly this up, now let me explain what would like to do with this. I'm preparing to buy 32GB of RAM and already have Quad Core. My idea is to implement another option in GRUB that will do exactly this:

1. On boot move whole / partition to ramfs, and boot ubuntu from there
2. From time to time and also at shutdown signal, run rsync to "backup" data to HDD, of course in background.

I already have SSD, and I think that rsync wouldn't take much to sync files. And also, loss of data is less important, except if it would be loss of more than 30 minutes active work, Because uptime of my computer is almost 99.99%, never turning off, so really don't think that this could get some bigger problem than forced power off from HDD.

/ filesystem is not much big, around 7GB.

Now my question is: Would this idea be "cost effective", would rsync take much resources, and is somewhere already implemented some similar solution of this?

At the risk of getting booted off for blasphemy...

Check out Puppy Linux. It works just like you are describing as it uses the unionfs filesystem or the newer aufs filesystem running entirely in memory. Though fully GUI, the O/S has been paired down to run in as little as 32MB (yes, MEGAbytes) of RAM or as much as you can give it. Anything over about 128MB will let it work entirely in RAM and thus be lightning fast.

Version 5.2.8 Lupu is compatible with Ubuntu 10.04 Lucid and Precise Puppy 5.4.3 is compatible with Ubuntu Precise Pangolin 12.04.1+.

rootramfs_0.2-1_all.deb

This package load root FS to RAM before startup system. For sync to HDD use rootramfs --sync sync_path [exclude_path1] [exclude_path2] ...

You can easy verify this package. Package contains scripts written in python, it fix initrd and cryptroot initramfs hooks.