Yeah it's very much a case of "who you listen to" - although I would discount out of hand any WikiMedia stats outright, as they massively over-inflate iOS stats to the point of lunacy, being about 2.5 times higher than every other source.
None the less, if Ubuntu makes good on its claim of 5%, my point is it's comparable to reasonable estimates of OSX, which are around 6-9% (probably 7% is a good estimate). 5% and 7% market share are not too different in my opinion, so it would be the first true sign of life for Linux on the Desktop.
My personal belief is, given the enormous popularity of Android (61% of US market, announced today, almost 75% of China and about 55% of Australia), the upcoming Ubuntu for Android (http://www.ubuntu.com/devices/android) options will make Linux on the desktop a reality; although in a way no one expected when /. first started that meme. Motorola is already working something basically the same and once people can easily dock their smartphone to a keyboard / mouse / monitor and have a windowed desktop environment instantly appear, I think it will really start to take off. I know for my work, I could probably do about 75% of my daily things like this - 100% if I include Remote Desktop.