Great site! Normally I hate sites that have overly-stylised navigation....but yours has enough charm to win me over.
Great designs, clean site. You've cut out the US/Asian/Australian market with the price (GBP 35 with P&P, about US$70), but that's still just about possibe within the UK market. If your marketing model could cope with cutting the price down to about GBP 15 a tee, you'd attract a lot more US/Asian/Australian sales, and the GBP10 international shipping seems a little steep (GBP airmail costs about that for 500g to the USA....which I seriously doubt is the weight of one t-shirt, unless they're lead-lined). I appreciate you post in your own gift-boxes, but even so...
I'd recommend finding your most attractive friends to model your shirts for the "Best Friends" section, linked to each shirt, before you get real photos in. You're selling in the top end of the market, and those people expect real-life images.
Your site design is actually quite similar in feel to our new site, which is one of the reasons I like it

.
But an excellent new site for our community! Welcome!