Using the same /home directory for two installations.
 

Recently I found out about Elementary OS Luna, and got the Alpha build, and installed it on my netbook, which has a 64GB SSD. Unfortunately, it often drops the wifi, or has a number of other annoying things, which are probably due to it being Alpha, so not fully tested. While I am reporting these bugs, I also use my netbook for development.
Unfortunately, this unstableness has been preventing this development, so I had the idea of installing Debian 6.0.4 GNOME along side.
Is there any way I can install them side by side, so they use the same /home directory, without them sharing gtk themes, and other nasty things.

You could do what I do - each distro gets its own partition with its own /home. My ordinary user has the same UID in each distro. On yet another partition, which is automounted on the same mountpoint in each distro, I keep folder containing the common files that I symlink into the home directory for my ordinary user in each distro.

A simple example in case my explanation appears to be confusing:
Partition sda6 contains the folder ordinaryuser_bin
/dev/sda6 is mounted at mountpoint /mnt/CommonFiles in all distros
In each distro, /home/ordinaryuser/bin is a symlink to /mnt/CommonFiles/ordinaryuser_bin

I found that using a common $HOME for all installed distros got a bit messy because of different distros using different versions of programs such as Firefox.

Hmm... I think I will give that a shot so I can dodge the problems with compatibility.

I don't think there should be any problem using the same /home partition for both distros. Just configure your fstab to mount the existing partition over your /home location.

What you should not do is share the same user between them. Since different distributions can have different paths, command names, etc, the configurations sitting in the user's home directory can get messed up. Always create a separate user for each OS.