Definitely negotiate for more time off! I am a recruiter and anyone who has been working for a couple years always ask for more vacation time. We can usually give up to 5 additional days, but if the person leaves the company they will only be paid out for the # of vacation days per our company policy at the time they leave. Our standard policy is 10 vac days, 3 personal days, 10 sick days, and 9 Holidays. You get bumped up to 15 days on your 4th year. Are you OK with everything else in the offer? If you are just tell them that the offer sounds great, and you are ready to accept but would like to know if it is possible to receive additional vacation days. Let them know what you currently get and see if they can make a compromise.