I somewhat disagree with Druuna on the issue of a common /home partition. The only thing you really need to worry about is making sure that if you are using different distros on the same machine, that you create new user accounts with different names for each one, and not try to re-use the same user name. An easy way to do this is to use an abbreviation of the distro name in the user name,... something like; johndoe_dbn or johndoe_ubntu...

By having a common /home partition, you can avoid reformatting your data if you install other distros, or upgrade in the future.
You just use the "advanced" partitioning option in the installer and refrain from formatting your /home partition on the new installs (after the first one)... and, of course, use a new user name... (you can migrate documents, pictures, etc. from the old account afterwards).

One thing you'll have to learn about is the permissions system in Linux... That defines who can access, copy, move or use a file or directory. It's also important to understand the difference between the terms "directory" and "partition."

A directory = a "folder" for files
A partition = a physical part of the hard drive set aside for a particular purpose, usually as a mount point (like for / or /home, for example) .

The /home "folder" can be either a directory on the main partition, or a partition of its own.

If you're not careful, this is just asking for trouble. Having to remember which distro I'm using at the moment and therefore the current username is a waste of brainspace. For consistency, I use the same username on each system (we are talking about home systems). Once I set up a different username on my netbook. Almost every day I made mistakes in (s)cp and other commands resulting from a wrong username. Why would I want to make my life unnecessarily difficult by having different username on each system? Btw, what if I tripleboot the same distro?!

I don't know. In the past I considered having a common /home for multiple systems but then decided that it's more hassle than it's worth. YMMV

For the record, I am using the same desktop, same flash drive, same everything. It's not like I'm doing this on 10 million different machines.

@sycamorex...

That's never been my experience... For me, the cost of having to recreate everything, and/or restore it from backups is higher than any user name inconvenience .... Plus, I usually change my Login theme to one that lists the users,... negating having to remember them,... except for those rare instances where I lose my X-server, of course... I usually define the user account by the machine its running on, adding that to the user name somehow.

I guess it's a matter of habits. My desktops are exactly the same (i3 tiling window manager) on all my Slackware installations. I don't use a login theme (runlevel 3). I don't keep many things in /home. All the preferences are backed up in ~/data/config including thunderbid directory and such.

Yes, but different distros use different versions of things which can cause conflict or issues. I like using kde, and some distros store the config file under '~/.kde' while others store it under '~/.kde4'