I'm sure that some of you are looking forward to that new Mac in a few days. Migrating from an older system to that new one can be a painless process. I just helped a friend set up a new 27" iMac, set up his old Intel iMac for his wife, and finally set up and move her old G5 iMac to their business showroom — all in about 2 and a half hours. In this case, we were able to work from Time Machine backups, so that I could work on all three computers simultaneously.
The first step was to check the backups. Both house computers had finished successful backups within 5 minutes of my arrival, so I was able to just shut down the systems and disconnect the drives. The new iMac was moved into position, Time Machine backup connected, and we started up. When a new system starts for the first time and the registration screen is out of the way, you are presented with the opportunity to transfer settings, documents and applications from another computer, a backup drive or a Time Machine backup. We selected Time Machine and set it to copy everything.
We then moved the "old" iMac to the wife's desk, and connected her Time Machine drive. We could have done a clean system install and started by reformatting the hard drive, but we decided to just migrate her files instead. I went to System Preferences > Accounts and created a new identity, and logged into that identity. I then started Migration Assistant (in the Utilities folder) and let it start copying everything from her TM backup.
While those two iMacs were chugging along, I started the cleanup on the G5, deleting old files and secure deleting personal data. When that was done, I set up a new, clean account, then deleted her old account from the System Preferences. We moved it out to the showroom, and set to work setting it up. No critical files are kept on the showroom computer as it is used primarily for printing shipping labels, so we haven't been doing backups. We still needed to transfer things like settings, bookmarks, printer drivers, so we once again ran Migration Assistant, which walked us through connecting the old computer in Target Mode using a FireWire cable.
By the time that was finished, computer #2 was also finished. We restarted it, and breathed a sigh of relief that all was functioning as expected. At this point, we had to open the Time Machine preferences and reselect the backup drive. It then gave us the option of erasing the backup and starting over, archiving the backup and starting over, or just continuing with that backup. We took the third option, and all is well.