iOS 4 Installed On 50% of iPhones

A recent survey by online ad network Chitika reveals that 50% of iPhones are now running iOS 4. iOS 3 is installed on 49% of iPhones, while the 1% remaining still runs the older iOS 2.

Looking more deeply, iOS 4.0 – the version released on June 21st – is the dominant single version at 44.5%. Version 4.0.1 – the latest official release for the iPhone 3G, 3GS and iPhone 4 – clocks in at only 5% of the market, not surprising given that it was released less than a week ago.

Seeing how slow iOS 4 can make your iPhone 3G, I understand why that many people didn’t update. Another reason might be that people want to keep their jailbreak. I’d be curious to know if iOS 4 adoption goes up once Spirit is released sometimes in the next few days.
What iOS version are you running on your iPhone?