Well like a lot of stuff on money.stackexchange there is not a simple answer, but generally it is not a good thing.
Take a look at the wikipedia entry on Net Operating Loss. Basically the company is commenting that when they do make money they will receive preferential tax treatment on that income.
So whether or not this is a positive or a negative depends on a couple of things:
- The quality of the NOL, i.e. is it some (legal) accounting magic that saves them money in the future, or is it really just that the company is doing terrible.
- The possibility that the company will have taxable income in the near future. There is a limit to how long the tax benefit can be carried forward and if they never make any money during that time, then they don't get that money as savings. At times continually unprofitable companies will have to write off these accounting benefits which can impact future earnings.
NOL doesn't directly impact book value other than how the actual assets of the company changed over the previous quarter. I believe there is a 1:1 correspondence to how the assets change and NOL, but I am sure someone could clarify that for me in another answer or as a comment.