I think it would be more transitional
If it where to happen, I don't think it would be an overnight change. You wouldn't arrive in the office Monday and suddenly the desktop market is 30% Apple, 30% various Linux distributions and 30% Windows.
Helpdesk knowledge would increase as the popularity increased. By the time a company did do a cold cutover, most of the helpdesk staff would probably have looked at it at home at least.
It also wouldn't suddenly grow in popularity without the end users becoming more familiar with it or at least it's availability.
Starter friendly distributions continuing to polish up user interaction with the system. if the reason for lack of polish is lack of consumer interest then growing consumer interest is going to drive distribution polish to the level of osX.
Trouble shooting would also improve as part of the continued polish in response to growing popularity. I have oddities on both platforms that don't seem to give any clear reason for being though too.
One definite benefit to measurable market share would be more support from hardware manufacturers, codec owners and similar areas where "it's not popular enough" is a rallying point. The user grief caused by this type of business politics now would decrease during the market growth.
As an overnight change it would definitely cause frustration on support and user sides. With measurable market share becoming more of a growth process I think the other issues around it would also be smoothed over as it went along.
It's also a chickenegg thing. Average users won't grow it's measurable market through purchases without universal hardware, games and other specialty software. Hardware and specialty software won't work with or develop for it until it become more measurably popular. Hardware may actually be motivated against it's growth as it doesn't force new hardware purchases as frequently as other platforms.
Apple remains outside the topic since they stick within there own hardware/software package as a desktop retailer more than an OEM developer.
Hopefully non of that seems argumentative.
