OK, we've talked about using Migration Assistant for setting up a new (or new to you) machine. But what else can you do with it?
Well, nothing says that the machine has to be a new setup. What if you want to add a user from another machine? Maybe you're selling a family member's laptop and don't have a replacement yet. You can use Migration Assistant to bring over that user and all the data in the home directory. Later, when you get another machine, migrate it back.
There's also nothing that says all the data has to come from one machine. You can use Migration Assistant to get data and programs from as many machines as you'd like.
I've been asked what "Other Files and Folders" transfers. If you have any directories created outside the normal areas outside of the User directories and the OS directories), this option will grab those files.
For example, I use software call "Fink" (no, really!) to install Unix and Linux open source software (there's another good system, too, called "MacPorts," and I'm sure readers will bring up others). Fink by default puts all its software in the directory "/sw" so that it's easily contained and can be moved/removed or whatever. Checking the "Other Files" option will grab directories like this one and migrate them to your new system.
If you are keeping both machines (the new and old) then make sure you change the name of the system in System Preferences/Sharing (or you'll wind up with "Jack's MacBook 2" or some such name).
Another tip: if you do have a previously owned machine you are setting up, you should wipe the disk clean and install the OS yourself. Why? Well, you don't know what kind of time-bombs are lying in wait on that system. Maybe the person you bought it from tried out some software and didn't like it, so they threw it in the trash. But that software may have installed things in other directories you don't know about, and when you go to put in a patch a year from now, surprise! Your system is messed up. Even if the stuff left over is benign, why let it take up space? Whack the disk during the install and you won't have to worry about any time bombs.
I've used Migration Assistant with every new (or new to me) machine I get – it's just too easy to transfer over all my programs and data. I've done PPC to PPC, Intel to Intel and PPC to Intel and haven't had any problems. So don't make moving your data harder than it has to be by doing it manually – use this tool that's already on your system.