Dude - somebody must be making a red cent (or more) off of any sale of this shirt, and regardless of whether you are affiliated with cafepress or not, unless you are actually affiliated with Slackware, I think you should be checking with Patrick V. as to whether or not he's cool with the idea of you selling this shirt. Not to be a buzzkill, but if you put as much time into something as Patrick has with Slack, I doubt you'd be wildly enthusiastic about the idea of some random guy coming along and selling T-shirts using the name of your project as the #1 selling point. If you think the "Slack logo with a pipe" is so cool, then why not submit your ideas to Pat via the Slack propaganda link, go here:
http://www.slackware.com/~msimons/slackware/grfx/
Seriously, I'm not trying to be a downer but if anyone wants to sell something using the Slackware name, Patrick's approval should be secured first. Maybe you have done that already; but based on your post it just looks like you are trying to capitalize off his work. -- J.W.