According to USA Today:
Overall, federal workers earned an average salary of $67,691 in 2008 for occupations that exist both in government and the private sector, according to Bureau of Labor Statistics data. The average pay for the same mix of jobs in the private sector was $60,046 in 2008, the most recent data available.
These salary figures do not include the value of health, pension and other benefits, which averaged $40,785 per federal employee in 2008 vs. $9,882 per private worker, according to the Bureau of Economic Analysis.
Thus, if these numbers are to be believed, federal workers on average earn in wages and compensation 50% more than workers in the private sector doing the same job. Bear in mind that the federal workers are paid by the private sector workers. We can't all be insiders.
The figures do seem large to me, however, and they do not correct for a variety of factors such as age or experience so take them with a grain of salt.