I work for DOD as a GS scale civil servant. All my active duty time transfered over (11 years). I paid 3% of my total accrued active duty base pay to Uncle Sugar in order to get credit for retirement. Generally, your federal retirement is calculated according to this formula: 1% of your high-3 average pay times years of creditable service. If you retire at age 62 or later with at least 20 years of service, a factor of 1.1% is used rather than 1%. I have 15 vested, 24 to go until I reach 65 for a total of 39 years or 42.9% of my base pay. In addition I pay into the Thrift Savings Plan up to 12% of my annual income and Uncle Sugar kicks in 5%. Free money is always cool.
Also, as a federal employee you can draw a reserve or national guard retirement (you cannot draw an active duty retirement and a federal employee retirement due to a change in the law). So I will be able to "double dip" a little. Also government jobs are much more lenient towards military service. And you are very protected as a veteran when it comes time to make cuts. Essentially you will be the guy locking up the last building in the government.