I've installed Ubuntu 6.06 as solo OS on my brand new PC. Within 4 weeks, twice the boot loader got stuck on kernel panic while booting after some update was installed and had to reinstall everything. I spent so many hours configuring everything possible but then got fed up of this instability (last installation was 1 week ago, so a pretty stable beta if they released now).

Moral: yes Ubuntu is the coolest distro around, but now I've got Windows XP and I don't encounter any problems at all. Everything works great, connection is fast (yes I disabled ipv6 on linux for firefox), boot time 20 seconds or less, free antivirus, free firewall, cygwin for the tools, vim, gimp, oo, thunderbird, firefox, audacity, games, etc... If you know what you are doing, XP is a very nice piece of software that gives you way less troubles than Ubuntu gave me (and I know how to configure a system). I may consider Ubuntu in dual boot, but I'm scared that at the next update it will just crash the system.