The t-shirt button doesn't exist yet, but when it does you'll definitely want to use it.
This button lets you tell me with a single click, "Make this illustration a t-shirt and take my money!" A disabled version of this button can be found in the cart section of each illustration for now. Once that button goes live, an announcement will be sent to the mailing list. (*cough* sign up *cough*)
When enough people have voted for that specific design to be a t-shirt, I will let mailing list members know that it's been made available for sale in this section as a limited-run item.
Flat out? I want to sell you one of your favorite t-shirts.
I don't want it to fade or chip after three washes. I don't want the seams to come undone when you put your arm through a sleeve. I don't want to use overseas labor. I don't want it to bunch in weird areas or hang oddly on you.
With limited-runs, I can justify the higher cost of quality materials and using a vendor in the USA by making you one of only a small group of people that will own that t-shirt. If you see someone else with it, you'll get to give each other a nod and knowing smile, like "Yea, we got one of these before it sold out."
That's beautiful, man.