I have been emailing my buyers for the last week or so about my move to Bidville. I just put in in the very small bottom of my emails on there purchase emails. Not pushy, just letting them know there is an alternative to Ebay. Word of mouth advertisment will get you futher than any other form of advertisment.
If you use the paypal packing slip, edit that too. I invite them to bidville, tell them I can give lower prices there, and offer a 10% discount on shipping.
Don't forget you can give a shameless plug 3 times a day on bidville community. It helps when you are trying to get his.