I'm sure by now that most people with an interest in Android and mobile technologies would have seen this video of the Linux on the iPhone guys running Android on an iPhone.
When I heard about this first, I wasn't sure that it would be worth changing the OS on the iPhone to Android. However, in this video you'll see that there is a dual boot option. Early days obviously, but it's nice to think that sometime in the near future you could have a real choice of which OS to use on your iPhone. Apparently, porting this to the iPhone3GS would take more work. For those with an iPhone 2G you can check out this tutorial to get Android on board your iPhone.
I'm in no rush to use Android on my iPhone. With the iPhone OS 4 on the way, I think that most of the issues people have with the iPhone will be gone. All that is, apart from the whole Terms of Service issue, which pretty much forces developers to use ObjectiveC rather than any of the useful cross compilation toolkits that have sprung up to support mobile developers.
That particular issue could be the tipping point for full Android adoption. But for me, I look at the broad audience that the Apple App Store reaches, along with the success of the iPad and can't see Apple losing any ground.
While we're talking about mobile, PayPal have presented an offering for the Android and iPhone app stores which would allow customers to pay for apps using their service. It's a clever step for PayPal to take, gaining a foothold in the booming mobile application economy.