If the Groupon isn't being applied to your item total, you may have items that aren't included in the Groupon offer. Check to make sure you don't have any iPhone cases, gift certificates, or sale items (noted by prices ending in $.95 or $.99) in your cart. In case you missed it on Groupon, here are the details:
Limit 1 per person. Limit 1 per order. Not valid until 48 hours after feature ends. Valid only for option purchased. Online only. Not valid for sale items or iPhone cases. Shipping not included; extra fee for shipping. Not valid toward gift certificates.
Threadless Help Team
Dec 5, 2012