Pros
The pay is far more aggressive than what you'll find on the GS scale for government work. The Fed straddles both the government and private industry fence, so you can get the best (and worst) of both worlds. Merit increases have been solid (even through the financial meltdown) and year-end bonuses make holiday shopping enjoyable. The benefits are extensive; health stipends, employer-paid pension, and a 7% match on your 401(k). Plenty of time off options between vacation, personal days, and the "snow" days when the rest of government freaks out because it *might* snow. Telework has taken off and some areas are two-three days a week. Promotions are tough once you hit mid-career level as no one seems to leave. Hence, it a waiting list to move up in your current role.
Cons
Best way to get promoted is to leave and come back after two years. Some divisions seem stuck in the 1950's (here's looking at you IT) and others prefer the bleeding edge. There is a fair amount of fiefdom and silos still exist. At times, it operates closer to a dozen private businesses (divisions) all fighting over the same scraps. Why? We turned over $100 billion to Treasury last year as "profit." Yes, some areas are content to let employees "retire in place" and get paid so long as they can still fog a mirror. Others run so lean an operation, the typical workweek is 7am-7pm, five days a week. Get your staffing levels right on both sides of that aisle.