Yes! If you log in to your paypal account (at paypal.com, not through your ubercart store) there is a setting of whether to require the buyer must have a confirmed shipping address. People change addresses so often, many of your legit buyers will not have bothered to confirm their new addresses, so you want this setting to be off (I suppose unless you only ship $10,000 items). In my case we were selling digital downloads at a few bucks a pop so this was a huge problem.