The problem is, their hardware is inflexible and overly proprietary, because of that reason they are not. The only way to get a flexible mac is to buy a pro series tower for a yummy $2000. We can still build raging high powered PC's for less than half the cost and we can get the hardware all over the place.
I don't think Macs will replace PCs in the workplace for a long time, so I don't think they are going to take over, at least not for a very long time. Also, they are kind of a rip off. You don't get nearly as much software made for them, apple products are way overpriced, a lot of the components are not up gradable or changeable, so you are forced to buy the new versions when yours becomes outdated. They look great on the outside, but for me I don't they they are as good and I don't think they will ever take over the market.
I'm a Big Mac Type of guy myself