Today I upgraded from Ubuntu 6.06 to 8.04. The process was fairly painless thanks to a guide I found floating around on the Internet by Ronald Bruintjes. Thanks!
I thought about posting it here, but that wouldn’t be fair to the author. So, please visit his site for more information.
However, be prepared to answer some questions regarding different configuration files. More specifically if you want to keep the original, or overwrite with a new one. I myself have edited a quite a few configuration files over the last year, so I had to do a manual screening before I decided what to do.