I should mention that I am in central New Hampshire. The seed was a Blue Seal sun/shade mix. The lawn is 6 years old and gets the right amount of watering/mowing.

Water. Heavily. Now. This is the one time I'd say that putting down 2" to 3" would not be a bad thing. In three days, repeat, and then irrigate at 1" a week until the weather's supplying at least that much.

You fried it. Unfortunately, re-applying fertilizer when it started to recover fried it worse and disallowed it any energy to come back with a second time.

I'd call it a 100% chance you lost at least some of it, and a 75% chance you lost most of it.

I'd plan to reseed this year after raking away anything that doesn't recover quickly. Fortunately we're just starting to move into the prime seeding period for the year. There's plenty of advice in other threads on that.

Scott you shouldn't be fertilizing at all in warm months with your cool season grass. Once or twic in the early spring, then another two or three times in the fall, but no summer applications.

Ok - after seeing morpheuspa's post I decided to act. I am ripping up the lawn and starting over. This is a great chance for me to remove the many stumps I have and to smooth out my many bumps. It also gives me the chance to dig out the stumps I allowed my builder to bury and eliminate the sinkholes that resulted from them. So this is a good thing!

I would like to install some sort of bent grass - I love the way it looks. I will create another thread looking for advice on that topic once I have some measurements. For now I am digging up stumps, heavily dethatching the whole lawn, sweeping that up and having at least 20 yards of loom delivered...

Woo, Bentgrass. You mean business, don't you? LOL
If you're gonna do it, please be sure to read up on how to maintain it. Bentgrass is not for amateurs. It is a very high maintenance turfgrass, so you want to be sure you will always have the time to devote. Because it is high maintenance, it's rather expensive to maintain. More than that, it is unforgiving.

Well then... Although I love the look of bent grass, maybe it's more than I should attempt. I want something that will make me say 'WOW' when I look at it. It needs to be durable and not terribly high maintenance - although I'm not afraid of a little extra work...

Proving there's a silver lining to every single cloud. Kill the lawn...take the opportunity to fix it up nicely. And it cost less than Roundup! Which, if you're going to refurb, would be a good idea to make sure the old stuff doesn't come back.

Bentgrass probably won't wow you unless you can care for it constantly. Personally, I'll spoon-feed a new seed bed because I don't have to do it for long. I wouldn't tolerate needing to do it to the entire lawn for the rest of time.

Like Bestlawn says, it's completely unforgiving of mistakes, too.

For NH, most people would suggest any of the cool-season grasses. Kentucky bluegrass, fescue, or ryegrass would all do well there. Any of them can give you a "wow" lawn if you work on it a bit.

Here in PA, I just got rid of my old lawn and put in elite Kentucky bluegrass--Midnight II, Bedazzled, and Moonlight. I don't know what cultivars would do best in your area, but others will.

Many dislike mixing species (after having done so, I'm in that camp). However, that can look nice, too, with work and very regular mowing.

If you could tell us about your yard (amount of sun, trees, etc.) we could give some more specific advice.

Before you launch into a reseeding project, please read up on it. There are lots of good threads here. From your initial post, it sounds like you are bit anxious and want to "do something" to fix your lawn - without too much though about what that "something" should be. That will get you in trouble with a seeding project even faster than with an existing lawn. You will need to resist the urge to put more seed out than recommended, water too much, fertilize too much etc. Just stick to the recommendations and you should be fine.

Scott,
As Bill said, do some research, it will pay off. However, you may want to get started soon. If you do decide to go with Kentucky Blue Grass, you do not want to seed any later than Labor Day up here in northern New England.

It takes 3 weeks for KBG to germinate, that puts you almost in October before it starts growing. Slow germination is a pain, but it is well worth it. KBG will make a beautiful lawn.

We know that October can bring lots of heavy rain, cold nights, even snow later in the month up here. Any of these will slow down the growth of you new seedlings. You want to head into winter with some good growth.

I renovated in September of 05 with Elite KBG and to this day I still have bare spots that fill in with weeds because I keep seeding too late in the season.

So this year I need to fill in a few spots, and a 9000 sq/ft area where we renovated our driveway. I am seeding tomorrow. Hopefully germination will take place around Labor Day and I'll have a nice stand going into October.

Good luck