I just upgraded from Ubuntu Feisty to Ubuntu Gutsy (which is still in beta). about 6 hours later, a couple of hiccups, and one or two fixes required for problems that I caused myself (and due to running out of hard drive space part way through), I'm running the new version. With all the same software still installed, and all my preferences and options exactly the same as before. Damn that's nice.
The really beautiful thing? Barely any thing's changed. A nice modification of the login dialogue for KDE (something that I've been wanting for a while, a user list), one or two new packages (GDebi for KDE is nice), and a couple of hundreds of minor upgrades that I don't really need to know about, or that I get pleasantly surprised by when I open up old programs. I can go about my business, exactly as before (how's that for productivity (wanker)), knowing that everything's just that little bit more useful, safer, quicker.
Thanks to the debian devs, ubuntu devs, and everyone who made all the packages that make using linux such a joy!