After leaving the update process overnight, my iPhone 3G is now running iOS4 (the backup process only took over 3 hours - is this a bug? Many other people are experiencing the same problem).
First impressions - underwhelming on the 3G device unfortunately. No multitasking obviously (not even fast app switching). Folders are great and I've already come up with a much more organised layout for my 50-60 apps. But no homescreen background for iPhone 3G? Why not? Can't help thinking I'm being nudged gently to get the new iPhone 4 by annoying lack of features (unfortunately I'm tied into a long contract so can't for over a year without great expense).
Not only are homescreen backgrounds not an option, but some of the fine art lock screen wallpapers have been removed, presumably for gallery licensing reasons. This is disappointing.
On the plus side, DarkFlow HD is up and running on a real device showing Apple's test iAds (real ads are scheduled to go live on July 1st). I have some more tweaking to do over the next few days, plenty of testing then I'll be submitting to the App Store. Stay tuned!
Update: being fed up with having some of my favourite wallpapers forcibly removed, I had a quick look on Google and found that at least one of them is available legally (public domain) on Wikipedia. Ha!