Don’t all new Macs have that new Migration Assitant that walks you through a transfer? Anyway, the simplest, fastest way to transfer files from Mac to Mac is called Firewire disk mode and requires a $10 Firewire cable. Here’s the how to from the Mac help docs:
You can transfer files easily from one Mac to another. If you’re transferring all your files from an older Mac to a new one, the easiest way to transfer files is to connect the two computers using a FireWire cable and use the Migration Assistant, located in the /Applications/Utilities folder. The Migration Assistant can automatically transfer your files and important settings to your new computer.
If you need to transfer a selection of files from another computer, you have several options. You can transfer documents, pictures, or music for use with your Mac OS X applications into the appropriate folder in your Mac OS X home folder. For example, copy documents into your Documents folder, music into your Music folder, and so on.
There are many ways to transfer files from one Mac to another Mac:
Send an email: Attach a file to an email message and send it to the other computer.
Copy files over a network.
Burn the files on a recordable CD and insert the CD in the other computer.
Use an external disk: You can use a Zip drive, portable USB or FireWire hard disk, or even a floppy disk if you purchase a USB floppy drive.
To transfer files to a Mac OS X computer using an external hard drive or CD:
Create a folder on your external disk to hold your files for transfer to a Mac, or insert a blank CD in your optical drive and follow the instructions on screen to prepare a CD for disc burning.
Select the files you want to transfer and copy them to your external disk or CD. To burn your disc, choose File > Burn Disc.
Connect your hard disk to the Mac OS X computer, or insert your transfer CD.
Open a folder on your external hard disk or CD.
Choose Edit > Select All to select all your documents.
Choose Edit > Copy to copy the files.
Choose Go > Home to go to your Home folder.
Open the appropriate folder in your home folder.
Choose Edit > Paste to transfer the documents.
Repeat steps 4 through 9 until you’ve transferred all your files.
To transfer files using FireWire:
Shut down the first computer and leave the second computer on.
Connect the two computers using a 6-pin to 6-pin FireWire cable. (If both computers have higher-speed FireWire 800 ports in addition to the standard FireWire 400 ports, you can use a 9-pin to 9-pin cable with the FireWire 800 ports to transfer data at higher speeds.)
Open System Preferences, click the Startup Disk, and click Target Disk Mode. (Or, start up the first computer while holding down the T key.) A disk icon for the first computer appears on the desktop on the second computer. Drag files to and from the disk to transfer them.
When you finish, eject the first computer’s disk by dragging its icon to the Trash. (While you drag, the Trash icon changes to an Eject icon.)
Push the power button on the first computer to shut it down and disconnect the FireWire cable.
If the computer to which you connect your computer is running Mac OS 9, it must have FireWire version 2.3.3 or later installed. Use Apple System Profiler (located in /Applications/Utilities) to check the version of FireWire installed. If it has an older version, get an update at the Apple FireWire website at http://www.apple.com/firewire.