How short did you cut it? The settings you mentioned are meaningless. How high is the blade when measured on a hard level surface? Even if you went down to an inch I really wouldn't worry about it. It sounds like your lawn is almost in its winter dormancy, so a short cut shouldn't be a problem. In fact many people recommend the last cut to be fairly short anyway, especially if snow mold is a problem. Of course you will have to wait till next year to know for sure, but I'm willing to bet it will be fine.

It went down to probably an inch. Should I seed it and put compost over it to be on the safe side?

You should be fine. If it's still green, you didn't kill it, but you may have stressed it a bit. If you want to mow shorter going into winter, it's better to cut back gradually, but going from a 3 to a 5 may not be that big (although as tiemco pointed out, we really don't know what 3 and 5 mean, so you may have gone from the tallest setting to the shortest, which would be less than fully optimal).

But for future reference, snow mold is rarely a problem in the intermountan west. You'd think it would be with all the snow we get, but with our humidity levels, it's actually pretty rare. When we do get snow mold, it usually kills a small amount of grass, but the mold dies off in a hurry as it warms up and dries out.

Since it's probably too late to seed, temps in the 60s this week, may reach 70, should I put compost down to add the nutrients I lost when I cut it too short.
I just want to ensure that my lawn will be great again in the spring. ;) Since our front lawn gets full northern exposure, when it snows, it pretty much stays on our front lawn forever (we are the last house on the block with snow still on our lawn till spring).
This is the first time I did this (stupid), I want to prevent it from dying or something.
I was so proud of the lawn this year.

Here's a picture of it. Probably not the best quality.

[IMG]http://i28.photobucket.com/albums/c249/penaddict/shortlawn.jpg[/IMG]

Trying to post again.

{{gwi:120775}}

I really think you are worrying too much about this. An inch is fairly short, but it isn't really a scalping. Your crowns are probably fine, and since your temps are low there isn't going to be too much topgrowth anyway, so your grass doesn't need to use much if any of its carbohydrate reserves to repair its blades. I wouldn't seed, or put compost down if it was me, the seed wouldn't have time, and the compost won't provide much in the way of nutrients now due to the low temps.