I'm by no means a Linux guru but I use Ubuntu 7.04 (Feisty Fawn) on a dual boot system with Windows 2000. Before that I used Fedora (core 5) and I've experimented with a few others but not used much. From what I can gather (and from personal experience) Ubuntu is the most user-friendly of the Linux distros however I still wouldn't say it's as user-friendly as Windows XP - very close though.
What do you want to do with it? I use my Linux machine just for general net use, email, playing music and DVDs. It works fine for that sort of thing but you don't get MP3 and DVD suport out of the box like you do with Windows. You need to install some software but it's all freely available downloads. I don't play games on my PCs so can't comment but I suspect you might have problems under Linux.
As Brianetta says, it's much less vulnerable to viruses, spyware, etc. Generally speaking bugs are fixed more quickly than with Microsoft SW. IMHO it used to be more robust than Windows but that was in the days of Win 98 and earlier. I use Windows 2000 at home and XP at work and find them both rock solid. It's still not perfect but then I manage to crash Ubuntu occaisionally as well - rare though.
Ubuntu 6.06 is a fairly old version and it's generally better to use the latest version unless there's a specific reason why you want an earlier one. That said, apparently there are a few problems with the new version of Ubuntu just released (7.10). One of the advantages of using Linux though is when something like that happens it's usually fixed in a few days by the Linux community as opposed to having to wait anything from 1 to 12 months for Microsoft to fix it in the next patch or service pack.
Windows moved my clock back too.

Now an operating system that could also adjust the clock on my oven, microwave, alarm clock, .... That would be progress!
