According to the American Customer Satisfaction Index, taxpayers who filed their taxes online last spring are happy with the results. Nearly 40 million of the 130 million individual tax returns filed in 2000 were filed online, representing a 13% increase over the prior year.IRS Commissioner Charles O. Rossotti, who is aiming to achieve 80% penetration in e-filing by 2007, was gleeful about the results. "The satisfaction with IRS e-file won't surprise any taxpayer who has used it," said Mr. Rossotti." When they try it, they like it.