yep i take it every day.
http://www.wmata.com is their website and it is really helpful.
you can buy a pass ($5 i think) for unlimited rides that day. i'm not sure if you can do it for longer periods of time. how much it costs you will depend on where you are starting from and where you are going, but it should be between $1.20 - about $3.00. unless you are staying out in the suburbs, your fares will be much closer to $1.20 per person.
oh and a word of advice. when using the metro escalators, stand to the right if you are not walking up them so people can pass you.
let me know if you have any more dc questions.
eta, i found more info about he special passes:
http://www.wmata.com/riding/passes.cfm
Metrorail passes
All Metrorail passes are gate-activated. The faregate activates the pass the first time it is used and prints the last valid date on the pass.
One Day Pass $6
Valid for one day of unlimited Metrorail travel on weekdays after 9:30 a.m. or all day on Saturdays, Sundays or federal holidays. Pass expires at the end of the operating day3 a.m. on Fridays and Saturdays, midnight on other nights.
7-Day Short Trip Pass $20
Valid for seven consecutive days for Metrorail trips costing up to $2 between 5:30-9:30 a.m. and 3-7 p.m. on weekdays. Pass is valid for any rail trip at other times. If trip costs more than $2, you must use the Exitfare machine to pay additional fare. Pass will be returned for continued use during valid period.
7-Day Fast Pass $30
Valid for seven consecutive days of unlimited Metrorail travel.