Computers are at that point I think where we are just starting to get used to having instant availability. Booting an operating system takes time. We hear every year about technology to eliminate the wait, but Windows, OS X, and Linux still require anywhere from 10 to 60 seconds to boot to a usable state.
Currently, instant on computing involves some form of hibernation where the contents of RAM are transferred to a non-volatile holding area (usually disk space), and restored on-demand when the system is needed again. SSD storage has made this much more practical. Operating systems and computer hardware have also progressed to a point where hibernation is more effective now than it was a decade ago. I know I personally never trusted it, after countless hard-resets when my narcoleptic computer refused to wake up.
The issue here is that most systems require rebooting at some point. Memory leaks, poorly written software that doesn't exit properly, and other issues make many OS's slow down over time. Windows was usually the worst at this, but seems to be getting better. My newest system, a MacBook Air, sleeps so well, and wakes so quickly that I reboot about once a month, unless I need to run updates that force the issue. I hope the industry can standardize on something that works as well as this. Then waiting for our computers to 'warm up' will fade away to memory with tube radios, and black and white TV's
If you do decide to use these features, please remember to reboot once in awhile, and be mindful of what you're working on when you pause things. Network-based applications do not always resume as well as local apps, and sudden disconnections while using Outlook or other server-dependent software can cause sync issues among your calendars, etc.