Windows 8 has hit the 40 million licenses sold mark just after the one month anniversary. This news was shared to the media at the Credit Suisse 2012 Annual Technology Conference. Right now it seems that Windows 8 is also outpacing Windows 7 in terms of the upgrades and this is mostly due to how the ease of use in performing the upgrade. The Windows Store is also seeing some decent numbers as it has pasted the $25,000 revenue mark and right now the developers of apps keep 80% of the revenues. So I would start developing for the Windows 8 platform.
