Well, I finally powered up the new Mac Pro, to replace the ancient Mac mini.
Great: Migration Assistant (via Time Machine backups) worked like a champ. I was originally worried how I'd bridge the Firewire 400 <-> Firewire 800 divide, but my TM drive had both FW400 and FW800, so the drive, itself, was the bridge. After that, and copying over all the stuff in my Bulk partition (1TB of photos, music, and videos), everything just freakin' worked. Amazing.
Beyond Great: Fast, fast, fast! Wow this thing is fast. Lightroom now feels almost as fast as Picasa! It's also remarkably quiet, compared to the Mac mini plus the two LaCie FW drives (each a 2-way stripe) I had running before. Now I just have three internal disks. Fast and quiet. [Also, remember that whole confusion about what disks to buy? Turns out that Apple's 1TB hard drive, at least in my machine, was a WD "Caviar Black" -- the same model I ordered from Amazon for my additional drives. This makes me feel at least modestly more comfortable that I did the right thing.
Annoying (1): For whatever broken fink-related reason, my /etc/ssh_host_rsa_key and friends were symlinks into /sw/etc/ssh, which didn't get copied over, even though the rest of /sw did seem to migrate just fine. That meant no ssh host keys, so sshd was very unhappy.
Annoying (2): I've managed to max out my five simultaneous iTunes authorizations over the years, despite not ever using more than one machine at a time. And, of course, the Mac mini is now powered down and disassembled. Real pain to bring it back up just to deauthorize iTunes. Instead, I tried the "deauthorize everything" thing, and it seemed to work. Amazing that vaguely copy-protected apps like Adobe Photoshop CS3 worked flawlessly, but iTunes made me jump through hoops.