Decided I wasn't buying enough on eBay plus to justify the membership. Went to cancel and was offered $30 voucher. Might stick around for that.
Under 'My eBay Plus' go to 'edit membership' and cancel. Follow the prompts and you should get a $30 voucher.
Your mileage may vary but it seemed worth the post. Might not work on young accounts, I've been on it for almost a year.
edit: Some people are getting long commitment dates for the voucher. Mine was a month but young accounts can be asked to commit for up to six months. This is better for older accounts with some tenure.