Depends on your salary and general lifestyle. Single with no kids helps. Commuting from the East Bay helps. Not eating out or having expensive hobbies helps. Not owning a car helps. Making more than the typical low-to-mid 6 figures helps. Not having an onerous student loan burden or consumer debt helps.

I've personally been saving over $2k/mo on an after-tax income of just over $6k/mo, haven't been trying particularly hard to max that out though.