I am using Ubuntu at work and I am equally impressed every time when I upgrade it. Upgrading the operating system actually works! I still remember trying to upgrade older Windows operating systems and I am not trying that again (must be said that this is some years ago). The Ubuntu Linux distribution is released as a major release about every 6 months. Inside these months plenty of the included packages and applications are updated. To upgrade from 8.04 (2008 April release) which is a Long Term Support (LTS) release to 8.10 (2008 October release) you must follow the steps here.
I have have one slight problem with some flickering when using alt+tab to change between running applications but I expect this to be handeled pretty fast. The frequent updates of the distribution (not a service release every leap year) is a very good thing.
I think Linux has become so simple that I am going to install it for my parents when I get them a new computer. Hopefully, they should manage. They already use Firefox and Thunderbird and I guess they should be able to use OpenOffice as well, even though … well you know how old folks are 😉