Try an iPhone, try an Android with Widgets, try an iPhone, try an Android again, you'll see the difference.
I'm on a horse.
And also: I really do hope the Desire's touch screen works as well as that of the iPhone..... It's the one thing the iPhone had over all other phones when it first came on the market; capacitive works a brazillian times better then resistive.....
Joyma said:SGS has noise cancelling, I presume so does Desire, dunno about iPhone, but that stuff is pretty standard.
WiFi on my Nexus is dodgier than my gf's iPhone 3G. Specifically, I have to manually reconnect to WiFi most of the time when I get home, whereas her Wifi "just works". YMMV.
About the UI, having used both phones a lot, I think the WoW UI is a perfect (and very cheesy ) analogy:
WoW's standard UI is like the iPhone UI: an amazing, thoughtful and very customizable interface that's smooth and buttery and designed down to the last inch while glossing over a few hardcore gameplay mechanics the average player won't ever care for.
Android is the interface for the hardcore raider with tons of add-ons, you spent hours setting it all up and it'll always be a bit rough around the edges, but it can provide you with exactly the experience, info, setup and efficiency you need.