Facebook is a dotcom bust waiting to happen...
Microsoft is the next IBM, they're just to big.
Someone will eventually come out with better marketable mainstream OS then windows, time frame I have no idea.
the next IBM? Well, IBM still has a market cap of over $200 Billion, so that worst case scenario is still 'aging titan', instead of 'dead' like the post's estimation. But MS innovated more than people realize, and their year over year profits are still growing at a very healthy pace.
As for someone coming out with a better OS - not only is it unlikely, it is irrelevent. Even if someone spends the BILLIONS necessary to build something better than windows, what good is an OS without software? You could come up with the best OS ever, and it's not going to make businesses give up everything they have to switch to something without software. It's not going to be enterprise viable for an additional decade. And gamers aren't going to give up their games. At best this OS would go the apple route - have some superiod niche products and get college students because it's cool. Meanwhile, windows continues along with over 90% of the global marketshare.
Also, MS has was more than just OSs. A few years from now, Azure is going to be one of their biggest profit centers - it's amazing.