Funnily enough, I'm posting this from my brand new Ubuntu 8.04 Hardy Heron install, I've got to say i'm actually pretty impressed with how the install went... (Hardy Heron was only released yesterday, and is a release that has a 5 year support scheme from Canonical)
I installed it using the new option of installing inside windows, it uses wubi(
http://wubi-installer.org/) to do this, and it works pretty damn well (I set a 6GB partition, as my laptop HD is only 40gb) when I boot up now I get two options, I can boot into XP or Ubuntu, and the best thing of all is that it didn't install Grub or any bootmanager... :-) Another key feature of installing ubuntu with wubi is that you can
literally un-install whenever you want... it puts an entry in Add/Remove Programs so you can remove ubuntu whenever you want - and as there is no extra bootmanager installed its all easy and works well.

Its found all my hardware (WLan needed a couple of re-boots and then propietary driver install) and i'm just pretty much liking the new release... I tried the previous 7.10 release but it caused nothing but havoc with my laptop, sound didn't work fully, wlan required voodoo to get it working, and graphics weren't that much easier... So the 8.04 release has been a breath of fresh air.
The only complaints I have atm are that there aren't many development tools installed... Python is installed but specifically Ruby isn't, but its a pretty easy install using the brilliant apt-get anyway...
Well yeah, I'm just pretty blown away by the new release... I've been trying ubuntu off and on since the 5.10 Breezy Badger release but 8.04 is just amazing :-D ... So yeah, as you can probably tell, i'd go with Ubuntu. And if you really still need windows apps, you can allways use VirtualBox to virtualise XP/2000 on-top of Linux, or of course you could use Wine to run your Windows apps.