If you regularly work with more than one Mac, you might look for a solution to keep your data in sync.
The most obvious way might be to use a server-based home directory if you own a Mac OS X Server. Yet, if you use this concept, each Mac has to connect to the server from time to time.
It might be challenging to put this into practice if your server is at work and your home computer connects using a slow modem (yes, this still happens) or if you are on the road and connect to the Internet using a Bluetooth mobile phone as a GPRS modem.
Another solution might be to directly connect your Macs to each other using a network or a FireWire cable to synchronize your data. Here I describe how to do this. Yet, this requires a fast connection again and doesn’t work properly with large files if your Macs are not in the same network.
The only good solution in these cases is to put your entire home directory on an iPod (or any other FireWire disk that you are willing to carry around all the time 
. To ensure that you always have a recent backup of your home directory, I recommend to copy your iPod data to at least one of your Macs whenever you work on that machine (here is how you do that). If your iPod ever gets lost or stolen, you can still access a recent copy of your online life.
If you are not scared to fiddle around with Apple’s NetInfo Manager, then go on and read how to set up your personal ‘home on iPod’.
First, create a new user on one of your Macs using the User panel in the system preferences:
Now create a directory on the iPod in which you are going to store your data. The easiest way is to copy the local home directory we just created to your iPod and to fill it with your data. You can put the folder in any directory on your iPod. According to the file structure of Mac OS X’s boot volumes I created a directory with the path /Users/iPod.
Now open the NetInfo Manager and enter your password. Select the user you created just now and change the value of the property ‘home’ into the path to your new home directory.
As the iPod is just another FireWire disk (in addition to all the other great things that it is), it is mounted in the directory /Volumes. The full path to your user directory on the iPod is /Volumes/iPod/Users/iPod where /Volumes is a static part of the path, the left name ‘iPod’ is the name of your iPod that you can see in the Finder whenever you connect your iPod to your Mac, ‘/Users’ is the folder I created on the iPod. If you put your home directory into the first level of the file system, just leave this part out. The ‘iPod’ in the end of the pathname is the folder name of the user’s home directory we created.
The whole thing might look like this:
IMPORTANT NOTE: If you enter a wrong path, the user might not be able to log in to your Mac or at least not to save any preferences or changes to his programs’ standard values! Make sure to have a second administrative account on your local Mac to log in using this account in case of problems!
Now you can quit the NetInfo Manager. It will ask you to save your changes and to update your NetInfo database. Say ‘yes’ and let it do this.
You just told your Mac to use an external home directory. Do the same thing with your other Macs. Now, if you want to log in as the user ‘iPod’, connect your iPod to your Mac, wait until it’s mounted and then log in. If you want to disconnect your iPod from the Mac, log out all users that have their home directories on the iPod, log in as a local user, and move the iPod icon to the trash. Now you can disconnect the FireWire cable.
If you want to copy files from other local users to your new home directory, it might happen that you don’t have privileges to read and write data in two home directories. Log in as root to be able to transfer the data.
Now the local directory /Users/iPod, that automatically has been created when you set up the iPod user in the users panel, is not used by the operating system anymore. You can delete it if you like. Yet, it can still serve you as a backup directory. In Mac OS X users are not allowed to read and write data in other users’ home directories by default. You can change these settings manually, but the already existing local folder ‘iPod’ has all the settings you need to copy your data into it!
So leave it where it is and synchronize your data between your iPod and your Mac.
If this seems to be too much work to you, use the local iPod user account instead (change the NetInfo settings back to /Users/iPod) to work locally and use the iPod as an external backup medium to synchronize your multiple Macs. This way you don’t have to create more than one local user per machine and you don’t have to log out and back in again each time you want to disconnect the iPod. Yet, the disadvantages of this method are, that you need a copy of all your data on multiple Macs and that each time you connect your iPod, first you have to wait for some time while you synchronize your data.
Please be aware, that you try this tip on your own risk!