I have an Atrix… it’s a very impressive piece of kit. The WebTop function definitely makes it unique - you can connect the phone to your TV via a docking station (sold separately, although I got mine free from Orange when I upgraded) and use it like a normal computer or media centre on the big screen.
Battery life is very good; I easily get 2 days out of it. I’d say I’m probably an average user, with a few calls a day and numerous texts etc. I don’t use any social networking services so I guess that probably saves a fair chunk of battery power.
I don’t know how it compares to an iPhone as I’ve never owned one but it certainly has everything you would expect from a modern Smartphone, and more.
One thing I personally don’t like about it though is Motoblur. The whole UI and especially the widgets are, in my opinion, incredibly ugly. I had a HTC Hero before this phone and if the Atrix had the Sense UI it would be perfect.