When Rackspace says 'four hour maintenence window' they mean 4 hours. Which is cool, but it was a bit unexpected.
Then they only had FreeBSD 5.3, not 5.4 like I wanted. It would have been nice to know that ahead of time, but that's just a couple extra hours.
So, Friday morning I have a working FreeBSD 5.4 up and running with an SMP kernel. It was very smooth. Then I installed all the packages it needed.
Next step was copying the machine's replacement configs over, which was not terribly difficult (yay version control!).
Then I spent several hours trying to figure out why apache wasn't logging. (Apache buffered logs + chronolog == suck).
mysqld decided it wanted to corrupt its user table for some reason, but eventually that sorted itself out.
Moving all our internal tools over was the hardest. Some of our stuff hasn't been touched/prettied in months. I found we had 3.2G of session logs, not because we had that much traffic, but because we had 3 copies of them! That is something to be remedied in the future. Now I'm down to the last step, wating for DNS to resolve and getting awstats caught back up.