I started to design t-shirts 3 years ago and since then, all my t-shirt have appeared in the top 50 of Redbubble.com, a 'print on demand' site with a international 'youtube' style audience. In the past 3 years I have had two designs in the number 1 spot and a design on nearly every page of Redbubble's most popular.
I also gained and still hold the accolade of having the most successful t-shirt on Teefury.com....
But I'm not boasting or anything ;-)