>>>But then you should adjust those estimates by the number of fashion geeks using iOS and Android for non biz reasons - not a mass market, but a sizable chunk of the smaller pie.
>
>OK, but those people are also a target for new breeds of app- e.g. multiuser mobile social media games.

Sure, but where do you see the marked difference to the mass market symbian users reason enough to single them out ? Over here the Outlook tie in gives them a large size of office coupled mobiles - but there are those music boxes trying to look like smartphones as well...

>Meanwhile MS has announced that its next mobile OS isn't backward compatible.

I view the inability to get a foothold in the mobile market as the first real problem in ubiquity MS is failing in.
Sliverlight is a concept to managing state in user apps across several distribution options,
but cloud services accessed via remote desktop and AJAX will nip from both sides, and if javascript enters server side via NodeJS in a way easier to overcome duplicating functionality server and client side, it will eat into PHP, RoR and ASP.Net all while keeping some out of Silverlight as well.
http://www.riagenic.com/archives/363
is another take on MS as focused as before.

my 0.02 EUR

thomas