Yeah I was blogging about it. Its a big problem. We don't want downtimes while you move hosts. Well talk a look at the tutorial then http://www.brainfeedlabs.com/web-dev/how-to-switch-hosts-smoothly/ Its pretty easy. Enjoy!
Actually those were just a few tips that are common knowledge, but if you're switching hosts, you need to switch the TTL on the domain to a low value before moving your nameservers to make sure the new ones propagate faster, so people won't be looking at the old site for 72 hours.