With the recent firmware updates Canon has gotten really smart about minimizing ink waste during sleep and wake-up. For example, the printers do a brief nozzle check (which doesn't require any any paper) and and wasteful head cleanings are only performed when needed. Performing regular nozzle checking in sleep mode also helps eliminate the need for cleaning. The latest heads have a teflon-like coating that goes a long way to prevent clogging too.
Although I haven't personally quantified it, the long term ink waste on a x100 firmware 1.35+ when left in sleep mode has got to be pitifully low. If a printer was left off for a while it is more likely to need a cleaning cycle upon startup. It's hard to say where the threshold might be for ink savings but there is head longevity to think about as well. I would love to see someone at the wiki quantify this with the x100 generation using the latest firmware.
It seems like a smart idea to leave these printers in sleep mode so that they can check and maintain themselves at the interval that Canon has determined to be optimal. Those that have left their printers unplugged for 4+ months while on vacation haven't reported any issues with clogging but have reported a need for a cleaning cycle. As to which uses more ink (letting it sleep for 4+ months or perform a full cleaning cycle upon return) has yet to be determined and will probably vary depending on your environmental conditions (temperature and humidity). I tend to encourage my clients to let their printers sleep and enjoy the simplicity of not having to mess or think about it. Thus far, print head longevity and ink consumption have been fantastic.
