other then when in an apple store I can only recall seeing 2 iphone 4's in the wild. I think it may have a lot to do with there not being many cases available yet.
I was in Las Vegas this past weekend and saw iPhone 4's and iPhones in general everywhere. I was at Aria, Palazzo, Venetian, and Hard Rock Hotel & Casino. Taking videos of the Strip at night was gorgeous on my iPhone 4!