There are already some pretty established t-shirt webrings.
To me, they are very 1990's. I don't think they work as well for bringing targeted traffic to the sites in the ring anymore because that's just not how people navigate websites anymore.
I started and managed one of the original t-shirt webrings way back in the day (t-shirts around the web) and ended up selling it a few years later (still in the 90's).
I think with the administration time (reviewing submissions, making sure everyone has their link up, helping with HTML to get the code on pages, server performance loading the webring stuff), it just doesn't seem worth the few extra hits it would bring.
There are better ways to promote your website that are more effective (search engines, directories, niche marketing sites, blogs, relevant links).
But that's just my opinion
Tshirt webring 
