Started with version 8.04 and updated everytime a new version was released.
Personally I love it. Some people dislike the mixing of open source and proprietary software, but I personally think it is needed to be able to reach out to the common man.
I like the Gnome interface, always prefered it over KDE.
Not that sure about the Unity interface used in the new netbook editions of Ubuntu.
Sure, it looks awesome, but today (02.02.2011) it doesn't feel stable enough.
I can't claim it to be the perfect replacement to Windows for 100% of the user case scenarios, but it's getting there.