I worked there over a year ago but here is the info as I remember :)
The discount is 40% ~ except on anything that plugs in at WS, then it is either 10 or 15% (cannot remember) ~ good at any of the affiliated companies and catalogs (PB, WS, PBK, PB Teen, PB Bed and Bath, Chambers, and West Elm). If you order a catalog item it HAS TO BE shipped to your home and NOT the store (sorry...no saving on shipping fees and surcharges). I do not know the hour requirements, although I am assuming that it probably varies from store to store (one store's minimum might be 16 hours whereas anothers might be 8, one store might require you to work at least one evening shift a week or a weekend day...you never know). It cannot hurt to call a store that you are not considering applying to and ask them :)
ETA: I have also worked at Restoration Hardware. I cannot speak for it now, as it has been over 1.5 years since I left, but it was soooo great. You can find a gift for EVERYONE on your holiday list there. They do not have any associated stores but their discount was also 40%.