FERS kind of has two parts. You have to have 20 years to get a pension from FERS (at least civilians do - I think some rules are different for active duty military) and the amount ends up being your number of years as a percentage (put in 22 years, you get 22%) of what your average base pay was for your final three years. Mind you, you get your BASE pay used - not any adjustments for location (i.e. I work in the Boston area so I get a 24% bump - San Francisco and New York, as example, are higher).

The second part is a 401K-like "TSP". Currently, I'm putting in 5% of my pay and the government is matching it (I get vested in either 1 or 3 years, I forget which). The primary difference between this and a 401K is that you only have a choice of a few index or bond funds to choose from.

One big change that happened some time ago but lives on in urban legends is that you can no longer use your accumulated sick time as a big retirement bonus. You lose your sick time at the end of your working days. HOWEVER - there is still one bonus. *If* you have enough sick time when you retire that using it would have bumped you across another 'year boundary', you can have your pension affected. In other words, if you worked those 22 years BUT had enough sick time that you COULD have made it to 23 years, you would get 23% instead of 22%.