Ok here's a little tutorial someone posted on another team:
1.) Register at www.stumbleupon.com either with Facebook or a regular e-mail.
2.) Choose some of their suggested interests so that you can have fun with stumbleupon outside of this thread :)
3.) Click the stumble button to get started!
4.) Go download the stumble add-on from here: www.stumbleupon.com/help/download_stumbleupon/
5.) Go to an Etsy page that you want to stumble and click on the thumbs up "I like it!" button.
If this page has already been stumbled, great! You're done! If not, a window will pop up asking you if it is "safe for work." You will also have the chance to describe the item and tag it. For tagging, just use the tags that the person had on their item. For describing, using the title works pretty well.
6.) You did it!
Some notes:
-To keep stumble from hating you forever and kicking you off their site, go stumble around the internet a little and "like" other pages you find interesting. Try not to make Etsy the only place you "like" on stumble.
-It seems like people enjoy seeing large photos of individual listings more than a shop page with a bunch of thumbnails. So if you're trying to decide between the two, stumbling a shop listing would be more beneficial.
