THINKING OF REFINANCING your mortgage? Welcome to the club. With mortgage rates so low over the past few years, the question hasn't been "should you refinance?" but "when"? While conventional wisdom once said you had to shave at least 2% off your loan in order for refinancing to make sense, these days it could be worthwhile with an interest reduction of just 0.75%, says Doug Perry of Countrywide's consumer-markets division. That's because soaring home values, increased competition and automated underwriting (which can approve or reject your refi application in a matter of minutes) have made refinancing quicker, easier and potentially...