One of the topics that gets the most heat every time a new Ubuntu release is out is that of Upgrading. If you take a quick look through any Ubuntu forum out there, you will likely see how most experienced users will advice not to upgrade to a new version, but backup your data and run a fresh install instead. In fact, I am pretty sure that most experienced Linux users will tell you to use a fresh installation. It is a fair statement, and a much safer approach.
Having said so, some times you have no choice but to take the upgrade route. Specially for corporations who stick to LTS (Long Term Support) releases and only upgrade once every 2 years, this is critical. Therefore, when you have to take the upgrade path, it is VERY important to get ready and be prepared for anything.
NOTE: This is by no means a Linux or Ubuntu specific thing. The company I work for now tests Windows Service Pack releases for weeks, even months some times. It does require a huge amount of effort and resources to find out how old applications will cope with new Windows releases or patches.
William Shotts has recently published two very good blog entries with advice on how to approach this upgrade process. With simple examples and very clear insights, I think these articles will help anybody who´s thinking of upgrading to Lucid Linx when it comes out next month.
Getting ready for Ubuntu 10.04, PART 1
Getting ready for Ubuntu 10.04, PART 2
I think these series will continue and involve more blog entries, so I would recommend following them up. However, even with the information provided so far, you have very good hints at what to look into. In fact, these activities usually have a lot to do with common sense, so do not simply follow these articles. Make sure you think of things which may be specific to your setup, and how you can overcome any issues that may be a result from the upgrade process.
Most importantly, expect no miracles from any upgrade process, regardless of the OS. Be sure to get yourself prepared!