We need to do ours now. We've owned the house for 5 years; not sure how long it's been since the previous owners did it last. (My guess is that it was a while before we bought the house.) We are in upstate NY.
Resealing is supposed to extend the life of the driveway, according to the guy that paved ours. Sealant keeps water from getting into the asphalt, which prevents cracks.
We did ours every-other summer in Minnesota. All of our neighbors did the same thing, so we would get together and do them at the same time. We would get a discount that way, since the company could get a bunch of jobs without having travel time between houses.
You can reseal the driveway yourself instead of hiring someone, but it's a PITA. We decided it was worth it to just pay for this to be done to save ourselves the time and hassle. We had a 3-car garage (fairly wide driveway) and we paid $85.
Awesome, thanks everyone. It's only a year and a half old now, so we'll seal for the first time next summer.
minniebee, we will be hiring out for just that reason. It doesn't cost that much and is a PITA to do, plus we have a ridiculously large driveway (110'x11' that widens to a 70'x22' area behind the house). A few of our neighbors look like they should reseal, so maybe I'll ask around to see if anyone wants to do it at the same time.
We just got ours a week or two ago. They suggested we seal it for the first time next summer and then every two years after that. We live in the foothills above Denver at just under 8000 ft. The climate is very dry.