Got mine last week. Have not used an iPhone yet but know it from friends. The biggest advantage I can see on side of the iPhone is the sheer number and quality of accessories on the market especially cases and the like. The selection for the Desire is very limited yet. Screen is fine. Apps are fine for what I need. Sound quality is fine. Don't have the problem with the ear setting off something while talking on the phone. Battery drain is proportional to what you do e.g. heavy use of internet will make you recharge daily but having it lying around as a dumb phone will give you 3 to 4 days I guess. That is similar to the HTC Tytn I lost last year.
I did not find any (sensible) use for the widgets yet. I find it far more comfortable to right go into the app than to use a limited widget which will open the app anyway if touched a little to long. Waste of screenspace mostly. I blame the quality of those widgets. The concept itself has potential.
I was first going for a Legend cause of the look and feel of the Unibody but since had the Desire in my hands I do net regret anything. Looks very elegant and feels solid. A softbutton for Menu and Back would be nice because the physical ones are way harder to press than the slight touch of the screen which can be an issue when using the device one handed.
The included 4 GB SD-Card is too small though. I leaves you only 1.6 GB left upon first start. That's plenty for apps but not for music or pictures or as a mobile data store. The 32 Gigs of the largest iPhone are something else here.
To come to an end: The Desire is a great smartphone. Buy it if you don't want an iPhone! You won't regret.