I have been putting off doing this for about two weeks, but plan on getting it done this evening.
What I will be doing is tweaking the new server's settings to improve performance. The downtime should be limited, say under 15 to 20 minutes, but I could run into problems. I will be compiling Apache again (the webserver), upgrading several pieces of software, and installing one or two new things to improve performance. I plan to start about 8 or 9 pm, EST.
The server is not usually too busy Friday nights, but right around its average. The best time for me to do it would be after midnight, but I try not to stay up that late often (Andy and Jenna are always up by 7 am). Also, if I run into problems, I want it not to be in the middle of the night - I can get in touch with my host's tech support easier.
Updates complete. Things are looking faster from where I stand. Hopefully that is true for everyone. Please let me know if you see anything weird. I am still doing some performance tweaking, which takes me watching the server, making a change, restarting the webserver or database server process, then watching again.