Ubuntu is nice and Linux in general is making very good progress as a desktop OS, especially in the last year or so.
And it'll keep on improving. Ubuntu itself has a strong 6 month release cycle... "Breezy" itself is due out sometime in october, I beleive. So by the time Vista gets out you'd already have 2 maybe 3 new Ubuntu releases.
That will include a ubuntu-style modified Gnome 2.12 desktop with some new features such as widespread use of vector-based graphics, improved file manager, and improvements in gnome default media applications. Here is a
preview of Gnome 2.12
Also we should see the inclusion of some interesting C# (yes, the Microsoft-created language) applications using Mono into Ubuntu. Applications such as F-prot (nice photogragh/image managing software) and Beagle (advanced desktop search application.) should be there by default... I think.
And that kinda help lays the groundwork for future releases were Linux desktop will move more and more gradually to being OpenGL accelerated and everything that entails.
Personally I am a Debian user. Ubuntu itself is based on Debian and is mostly so-so compatable.. they take a snapshot of Debian unstable then build Ubuntu's extensive mods and usability improvements on top of that. Lots of docs from Debian.org and such apply to Ubuntu and any power-user should be sure to check those out on how to get the most from apt-get and such.
Also since Debian and Ubuntu are simliar then Debian 'Stable' (currently Sarge) on a home server should make a good compliment to a Ubuntu desktop.
For isntance what I do is that I have a seperate file server setup from my desktop. It has 256megs of ram, a 2400+ AMD cpu, a intel gigabit network card, a 120gig WD harddrive connected thru the motherboard's PATA interface, and 2 120gig Maxtor drives hooked up thru a SATA controller plugged into a PCI port. Using Linux software RAID (technically known as Linux 'md'), I have those in a RAID 5 configuration with linux LVM (logical volume management) on those so I can resize and manipulate the partitions while they are running (more or less).
Although it would of been much simplier to buy one or two bigger harddrives...
It makes a nice setup. With the gigabit network it's as fast, and maybe even faster, then local storage on my desktop (just a 80gig wd). If you like to dual-boot with windows it can be handy because you can put you music/movies files on the server and have them aviable to both OSes equally without having to resort to any extra fat32 partitions.
Then if you want to get fancy you could have it do some streaming media stuff, or maybe use it as a remote web-controlled jutebox. I have mythtv and a video card on mine so that I can record shows and such (but you have to be carefull that the mythtv backend and frontend on your systems are the same version) so I can do things like watch TV on laptop as I carry it around the house or go outside and such. Or you can use it as a webserver or whatever you want. Linux also makes a great game server if you like to have lan parties and such, most games even if they don't have a linux client have a linux server aviable for it. Hell, you can even use Asterisk@home to create a corporate-style PBX for your home. (make calls over VoIP on a veriaty of formats, use regular telephone lines, email faxes to yourself and to other's fax machine in the form of PDFs, have 'put on hold' music, all sorts of stuff) (note that asterix@home is it's own distro based on CentOS that is based on Redhat ES, but you get the idea..)
Some of the stuff is very difficult to do, but it's fun if you like to mess around with computers as a hobby. Almost every peice of technology that is aviable and is used by large corporations and such is aviable to you in one for or another in Linux at no extra cost so the sky is the limit.