You cannot stay at 18F for the long term. These are limited term, 'non-competitive service' positions.
* Job security only for your 2 year term (unless you renew by another 2 for a max of 4 years). After that, you need to leave government service
* Health care coverage was similar to major tech companies in the Bay Area. However, vision / dental benefits were worse.
* Pension benefits only start after 3 years of government service, so most working for 18F will likely not receive these.
But I agree that for other government positions these are good perks.
18F's problem is that the appeal of government work is in benefits other than salary: solid health coverage, a pension, job security. But those are really only of interest if you're planning on staying there long term, and 18F's pitch has always been "take a year or two off from your real job and come work with us." It's the Peace Corps for techies, and nobody joins the Peace Corps for the retirement plan.