If the rumors of a small upgrade are true AND they wait until September, I see a lot of people with upgrades switching to Android devices. Sure, 4G isn't even available in most areas, but 4G is the hot new thing, and to people who dont really know about stuff like that, a 4G phone is way better than a 3G regardless of whether they can make use of the 4G network or not.
I am not sure about the US but the UK has not got the capacity for 4G yet and I think people are savvy enough to know whether they'll really be able to take advantage of it.
The big question I think is whether the small upgrade is true and if it is, you are right, people will flock to android because iPhone will be too far behind. The 3.5" screen is outdated, really outdated. I can't imagine going to android but the SG2 has certainly got me thinking.