Sorry, but am I the only one here seeing this as a software update you have to pay for? Fair enough, it's very "cheap" compared to previous OS releases, but it's still expensive compared to other pieces of software out there. Costs the same as Pages, and many people don't get Pages because they think it's not worth the price.
The best feature is probably airplay and powernap, but those only work with the most recent macs.
Finally, nobody is taking into account the time it'll take to upgrade and the loss of productivity during that time. Upgrading to Lion took me ages, needed spotlight to reindex, timemachine to do its stuff as well, but at least Lion was more of an upgrade since it changed the way you use a laptop completely with the full screen applications.
It's not that expensive if you consider how much a company in Redmond charges for the equivalent operating system. I'd rather spend $20 every year rather than a much heftier sum every three years. Also, you can install OS X on multiple systems using the same Apple ID.
Moreover, you don't really need to spend $20. I'll be spending $16 for my copy of OS X Mountain Lion using a totally legal method since I've figured out how to game the iTunes/App Store system.
I think most people will understand that there is some loss of productivity when you make a major upgrade. However, most people will have a greater productivity loss getting their haircut or going to the dentist. A level-headed person would just write off this time as required maintenance, like getting the tires rotated on your car.
Since it hasn't dawned on you yet, let me offer a suggestion. Install the upgrade and then go do other things. Go out to dinner, go to sleep, play with your kids, go to the ballpark, etc. No one is forcing you to upgrade during the busiest part of your workday.
Me? I'll probably download this morning, then wait until tonight or tomorrow night to upgrade before I go to sleep.