The move is complete, and everything seems to be fine. DNS was configured by some brilliant sysadmin (yours truly) to expire after only 30 minutes, so the transition was pretty much transparent.
I've definitely gotta hand it to Earthlink. They managed to underpromise and overdeliver on this one. They didn't give any timeframe for the install, so I assumed 2 weeks or so…they did it in less than a week. They promised 1.5Mbps down and 128Kbps up, and delivered 1.5Mbps down and 256Kbps up. It took a bit of savvy to figure out how to reconfigure the DSL modem so that my server would come online, but a little bit of tinkering and it was a done deal.
Now I can breathe easy (fortunately the mail server upgrade I did this evening went smoothly, too!)