There's usually a lot of confusion about what the new stats are showing and where Android is at some point in time, and that's because they are not all showing the same thing. One stat could show total subscriber numbers for US (like this one), another could show total subscriber numbers globally, another could show the number of sales only for the last quarter in US, and another could show the number of sales for the last quarter globally.
These numbers can't all be the same when shown as market share, which is why sometimes you'll see a bigger number for Android, and other times you'll see a smaller one, and you'll wonder what happened, but you have to keep in mind what each piece of data was showing at that time. That should remove the confusion.
The numbers we have here now from ComScore are showing us how much market share each company has gathered with their own operating system(s) over the years, in total (very important aspect). As you can see in the chart above, Android has reached 50% of the users in US, surging way past the iPhone, even though it had a severe handicap in number of total users when it started, compared to the iPhone and iOS. Also both of them have surged past other "legacy operating systems" such as Blackberry OS and Microsoft's Windows Mobile (their numbers also include Windows Phone 7, here).
Compared to the previous quarter that was monitored by ComScore, Android grew 0.8%, Apple grew 1.7%, Microsoft's operating systems grew by 0.1%, RIM lost 2% and Nokia with Symbian lost 0.4%. So what do these numbers mean? It seems Android is going to gravitate around 50% of the market in US, which means that out of say 100 million users, 50 million of them would have Android devices. Again, this is the total number of Android users in the market right now. Android growth in new sales is at least as big percentage wise, which means Android will continue to have at least as many total subscribers in percentage for the time being.
Even though I think Android will reach 60% or even 70% of the global market, it will probably remain around 50% in US, because of Apple's head start in US, and Americans' general love for anything Apple. Apple's brand is just much stronger in US than it is elsewhere. Apple is seeing some healthy growth in US, gaining 1.7% from last quarter, and they will probably each 35% or even 40% eventually, but I doubt it will be more than that. The other operating systems besides Android and iOS will just have to fight for scraps.
Microsoft saw 0.1% growth, which is the first time their market share doesn't decline in a very long time. Keep in mind though, that these numbers show both the Windows Mobile total subscribers, and the WP7 total subscribers as well, combined. Each should have about half of that 4%. But at least it means that the Windows Mobile decline is not bigger than WP7's growth right now. Microsoft will have to do a lot better than a 0.1% growth per quarter if they ever hope to pass the 10% mark by 2050, though.
RIM has been losing around 2% or more per quarter for the past 2 or 3 years, and since they never really took it seriously, because they had international growth to compensate for the decline in market share in US, they are now in a terrible state. They are now at 11%, and next quarter they should be under 10%. By the time BB10 launches early next year, they will be close to 5%. They'll need to blow everyone away with the innovations in BB10, if they hope to ever recover from that position, which I doubt will happen.
Nokia saw a 0.4% market share decline for their Symbian operating system in US, and is not like it was very popular there, but it's hard to tell if the Lumia 900 did anything to compensate for this loss. Yes, Microsoft saw a bit of growth, but that's with all WP7 phones put together, not just Nokia's. At best they broke even, and now that everyone knows that it won't be upgraded to WP8, their sales will fall for the next 1-2 quarters.
Besides, the only reason why they had some moderate success with the Lumia 900 was because of the phone's design, not because of WP7, because it had the same version of WP7 as many phones released months before. Who knows what will happen if their next phone won't have such a great design. Maybe they need to put that contingency plan in action, and switch to Android before it's too late.
To sum it up, it looks like Google and Android will dominate the mobile market for a long time, with no real competition in sight for at least a year or longer, while companies like RIM and Nokia will continue their decline, and maybe even be acquired in 2013, because the rate of their decline is unsustainable.