For $10 + ship, I'd buy it.  For $15 + ship.... not so much.  I didn't know about shirt.woot until yesterday.  Looking at the sales stats it appears the cool shirts are gone by 1:30am on average.
Well, what would you consider is a reasonable shipping cost?  How 'bout free?  Even when they sell em for $15, the shipping is free.  Not a GREAT deal, but certainly not bad.  And yep, if its a popular shirt, it sells out pretty fast.  Same thing with the main woot item; if it's cool, it's gone fast.
here are a couple of other arcadey shirts that woot has sold:
"Sore Thumbs" (looks like its sold out for good)

"Space: The Flattened Frontier" (still available)
