There are over 4000 open issues about JIRA that people have voted for. The most popular vote has 592 votes but most issues have zero votes. I found a suprisingly good line to fit the data with a correlation coefficient 0.9882, if Excel is to be believed. I'm not sure that I actually believe in predicting what people vote for, but I guess this is one way of measuring your progress is how the coefficients of the predictor change over time. The flatter the line, the better job you are doing of evenly spreading out customers' irritation with your product.
As of July 2010, the coefficient of irriration for JIRA is -0.65.