Nearly 15 years,I had backed up FDD/CD/DVD image+patch+fixedexe neatly.
Backing up cost me time,space,money and energy.
Recently I stopped it,because of online game stores arising.

Basically,I don't backup until each business raise question about its future.
Steam is highly prosperous,it continue at least more three years.Therefore I don't care it,but never depend on it,and don't buy games supposed to play many years away,such as wargame/strategy/roleplaying games.
GOG is stable business,it will continue long years than other download shops.I wait game release on it if don't want play soon.
Indie bundle need to back up,if it deserve cost.
GamersGate is unpredictable.Paradox have loyal customer in its core like Matrix games.But their business is unsteady.

Even giant company don't give assurance their service lasting for many years away in gaming industry.But backing up drain your money,time,and energy.It's waste of life.
We need strategy on it.

The only Steam games I backup are the DRM-free ones like Commander Keen and the Sega Genesis collection. Tracking down cracked executables and testing them is usually too much bother.

I would (and do) buy all the cereal flavours that I'm likely to want to eat. And all the soups, etc. Same thing with clothes. I don't schedule what I'm going to want a few days from now.

It's the same with games. But with games, once they're downloaded and backed up, I don't have any more work to do. It baffles me that people think there's additional effort to do this. In fact, there's less effort. I spent a measly $200 to get a 3TB disk and I don't worry about figuring out what to delete to make space for the next game. Who cares if some games just sit there for months without being played? They don't bother me. And if I feel like playing them again, as it often happens, I don't have to waste time and bandwidth downloading it again. It's deleting things to make space and downloading games when you feel like playing that's a waste of time, not what I do. Even the backups are practically a freebee. It takes a couple of seconds to start the copy and then I'm covered and I don't have to worry about what might happen to my main disk. The 3TB disk dies? Pfff! I swap in my backup disk and I'm up and running in minutes. Then, I buy a new backup disk, copy the stuff to it overnight, and my troubles are over for the next few years. No worries, no hassles, no time wasted.

I do not really backup any game.

If some service where I own some games goes down, and I want to play the game from there, I will simply download the game from somewhere else, be it gog or piratebay.
I will definitely feel perfectly fine doing that.

I just recently started backing up mine on DVD, since a lot of my games are actually Steam independant, or if they aren't I can make them be! :p