As some of you may be aware I had recently shifted one of my big sites from dreamhost to hostgator.
Moving webhosts is always a painful process, I have jotted some points below from my experience which may help you move from one webhost to another in a seamless manner.
- First things first – Change TTL for your domain to some very low value ( at least 2-3 days before moving) so that DNS propagation could be very fast.
- Some people suggest to add the new name servers at #2, #3 priority to your older webhost name servers panel.
- Create a new database at the new webhost and assign a user to it. It’s always a good idea to use a fresh database for a given site.
- Make sure to update the MX records in your new web panel. This is important otherwise your domain specific emails won’t work.
- If your host is hostgator and you use Google Apps, make sure to ask hostgator to open various ports. For security sake, many ports on Hostgator are either completely blocked or are only available for outbound emails. You can use a query on SSH telnet mail.authsmtp.com 26 to check for example whether the port 26 is open for mail.authsmtp.com. Similarly telnet pop.gmail.com 9595 to check port 9595.
- Configure various cron jobs you may have created earlier.
- Change the database info on your config.php files. I had to change at 3 locations dap-config.php, osticket and wp-config.php
- Make sure your DNS settings looks the same as they were with your earlier webhost.
Bonus: Here are some commonly used port numbers available for Hostgator
What other precautions/tips would you suggest while moving webhosts?
Ankur Jain is a Software Engineer in Test Automation. After a 5 years stint with Accenture and Oracle, he started his eLearning company. A long-time blogger and proud owner of the "Learn" series of websites. 
Good points but I think there are some online tools which you can use and that can transfer your website from one host to another. Hostgator is really a great hosting company and I think they can also help in transferring sites.