What happens? Nothing. Absolutely nothing.
What happens to the companies themselves? Nothing. What happens to perceptions? Probably something. There's always mistrust of the biggest player. If Apple become's the most valuable technology company in the world, their propensity to control their stack will be even more a focus for the media. I think Microsoft will relish being an underdog for a change: "Clearly we're not a monopoly. We're not even the biggest tec…
For one example: one of my business clients has a couple of die-hard Mac users (who I'm happy to support), and the administrator there is one of those "bah, Macs are toys, why don't they just get a PC like everyone else?" idiots. I mentioned to him one day that Apple had enough cash in the bank to purchase Dell outright. However, this did not at all change his perception of Apple.
It doesn't help that many individuals' exposure to Apple right now is through consumer devices like the iPhone and iPod, and not so much through "serious" computers.
Oh, and also: software. I'd hazard a guess that most of my clients don't think of the stuff on their iPhone as software in the sense of "stuff that runs on a computer". I suspect that they think of it more as "features", so for them, the only Apple software that they know of is iTunes.