I've been using Ubuntu Linux for a little over a week now, and here are my first impressions.
First of all, although I haven't had a chance to use KDE yet (it comes with a separate version of Ubuntu called Kubuntu), I'm really liking GNOME. It's similar enough to Windows to make it easy to use, but it has heaps of features that are the sort of thing that you always wanted in Windows but never had. Things like being able to drag and drop icons anywhere instead of just in the "Quick Launch" section.
I've also come to enjoy having access to a decent text-based shell. apt-get and the Synaptic Package Manager are an interesting way of dealing with software; it seems to work well with the software that is available for Ubuntu but I can't imagine it'd work that well on a system like Windows with so much software available for it. It's also nice to have a shell that's so much more versatile than what Microsoft offers (which doesn't even really have a name). Pretty much any task that you would want to automate can be automated in Linux via bash scripting.
However, I think it's somewhat short-sighted of the developers to cripple access to "non-free" software, or software that isn't correctly licensed to be distributed in the Ubuntu package. You have to go out of your way to enable access to the repositories that store any non-GPL code (at least I think that's what you have to do, you definitely have to specifically enable a repository to access proprietary code like nVidia's drivers, or Opera). There is a lot of software that should be included with the OS but can't for legal reasons (or maybe philosophical ones); my opinion is that a program like Automatix should come pre-installed, inform the user of the difference between the different repositories and get them to pick the ones they want, then offer to install some important software that isn't pre-installed. For example, graphics drivers for nVidia/ATI cards, VLC (the "Totem Movie Player" that comes pre-installed is useless, as it relies on the GStreamer framework to play media, and out-of-the-box can pretty much only play Ogg-based formats), and maybe even Opera.
One thing that does suck a bit about X-based Linuxes is the amount of time you spend editing xorg.conf. To be honest, I shouldn't even have to touch this file. In order to change to 1440x900 screen resolution (for a commonly-available 19" widescreen monitor), I had to edit xorg.conf. This required me using the terminal (as superuser!) to backup the configuration file and then edit it manually, which I think is too much to ask of your average user considering that screwing up this configuration file drops you back to a terminal. If you don't know bash and you don't have an alternate PC to troubleshoot from, you're SOL and need to reformat.
I'm also struggling to edit xorg.conf at the moment in order to fully set up my Logitech G7 (I'm following this tutorial on the Ubuntu forums). It's a great mouse, by the way.. the only wireless mouse I'd ever consider, since you don't have to continually replace batteries, nor do you have to leave it to charge overnight (leaving you without a mouse until it recharges if you ever do run out of batteries). It comes with two 'hot-swappable' Li-ion batteries that can be swapped within a matter of seconds when you do run out of power. Unfortunately, this happens pretty frequently - the battery life is only 5 hours or so - but I suppose that's what you get considering the size of the battery and the fact that it's a high-res laser mouse. There's a battery indicator on the side of the mouse, but it would be nice to set up some sort of battery monitor within Linux. The crappy Windows software has such a feature, but it's a bit of a RAM hog considering the tiny amount of work it has to do. The Windows software is also required to use the side-scroll, which is what I'm trying to set up at the moment. I've run into a dead end though, with X claiming it can't find the "evdev" protocol or something. The mouse did work just fine as a regular three-button mouse with scroll straight out of the box, though.
Opera (my preferred browser) just isn't the same on Linux. Things like middle-click act differently, and to be honest, I like using it better in Windows. It looks a lot better, too. Opera doesn't integrate so well with GNOME.
I haven't yet attempted to share or print over the network. We'll see how it goes. Something that did disappoint me was how difficult it is to print to PDF. I would have thought Ubuntu would have a menu option integrated into the default print dialog.
One strong advantage of Ubuntu is that you can just put in the LiveCD and boot off it (not unusual for a Linux distro). However, you can actually install the full OS onto your hard disk using the LiveCD. It even includes a great GUI partition editor, so that you can dual-boot Windows, and preinstalls GRUB for you. The only complaint I had with the install was that it installed GRUB onto my IDE hard disk, which I don't boot from. This was because the default option was to "Install GRUB onto (hd0)". I could have changed the option, but at the time I didn't know what hd0 even was, let alone know enough to manually type in sda instead (this is my SATA boot disk, but there was no drop-down menu).
I'm also considering removing AdSense from this blog. Really, it's not like it brings in any sort of significant income (I'm yet to receive my first cheque; I think you need to make $100 first) and I'm not sure whether the potential of maybe some day getting a $100 cheque from Google is worth the ugly ads. This blog is more-or-less a place for me to rant, anyway.