Once you have been to a Cirque du Soleil show, you just can't help paying attention whenever they are mentioned from then on...
2009 will be the 25th year of the cirque du soleil and the 25th unique show they have created over the past 25 years. Take a look at their anniversary site.
I had the pleasure of seeing Alegria in New York and spend a few evenings with Cirque du Soleil employees. I can't remember ever having seen so many people being simply impressed by the simple Cirque du Soleil jackets they were wearing, just to give you an idea of the effect they have once you know and have seen them.
If you ever get the chance to take part in a live performance like the one below you will realise why people talk about them in this way (Montreal Jazz festival, Soleil de Minuit, here):
See also the intro song from Jorane for the Cirque du Soleil show at the same jazz festival show. really gives you that beautiful bohemian, cirque atmosphere: