Threadless's website is quite funky and their strong point is really the high-quality images of their designs with amusing fashion-shots of people wearing them. I browsed their complete collection of t-shirts and chose three that caught my eye: A Scent of Doom, Women (the look on this guy's face sold me on this one, gold), and Fluttering. The designs are all made by members of the site and most are very imaginative and skillfully designed. There seems to be a bit of everything, though I would say the graphics tend to lean toward a kind of retro-techno crowd.
After choosing my shirts, one slight annoyance I had with the website checkout was that I couldn't bill my address to Canada and have it shipped to France where I'm currently living. I shot off an email right after ordering asking if they could manually do it and just charge me the extra shipping amount, but I held out little hope of getting a response. Less than an hour later, this email arrived in my inbox:
I've changed the shipping address for you at no extra charge, but in return you have to tell 50 people about Threadless.com and sing it's (sic) praises all holiday season.

Don't forget, though, that your order might take a little longer to reach you in Europe than it would if it were going to Canada, so be patient.
That's pretty awesome service, and hopefully 50 people will read this review and satisfy my end of the bargain! The shirts arrived quickly and when I unpacked them I wasn't disappointed. The shirts are Fruit-of-the-Loom* and screen printed with 3 different spot colours. The quality of the screen print is impressive and the colours of both the shirts and the prints are vivid and funky.
Another neat thing about Threadless is their "Street Team". As a kind of alt-advertising, they have a program set up whereby you can win street-team credits toward future purchases. While this might seem like shameless self-advertising (of course it is) it's also fun, well conceptualized, and truly rewarding. After only referring 5 sales to their site, you get a free shirt, pretty good payback, especially if like me you're happy to promote them sans-reward anyway. Needless to say I'm signed up and am starting to spread the word.
Threadless really seems to be a tightly run ship with an excellent product and wickedly-good customer service. With new designs popping up every few weeks I'll be sure to check back. (I know this review oozes of sucking up, but everything went so smoothly with my order that I can't help it.)
* Only one of the shirts I received in the mail had a brand-tag on it (which was Fruit-of-the-Loom), but they all appear to be the same. That said, I put my American Apparel t-shirt next to it and they look exactly the same. I mean, right down to the way the double-stitching goes around the neck and arm, they looked identical. I'm not quite sure what the deal is with that, but they are really high quality shirts nonetheless.