I've had my E71 for about 6 weeks now, and I thought that I'd write a few words here to let people know how I'm getting along. Would I recommend the E71 to anyone who is looking for a smartphone? Absolutely. Would I recommend it over the iPhone? That depends. If battery life is important to you, then certainly. If productivity software such as word processing, spreadsheets, etc, then yes again. I'd even say that the camera on the E71 is better than that of the iPhone (based on shots that I've seen on Flickr).
However, I have found the breadth of software available for S60 series smartphones to be somewhat lacking. I've spent ages looking for a native Twitter client (not J2ME) and I've only found one (WirelessIRC + Twitter), which is an add-on to an IRC client. The iPhone has lots of clients, many with their own twists on user interface. [Update: As of May 2009, there are a few more options, one of which, Gravity, is superb!]
However, I have a nice core of software on my phone that do most things that I would want to do whilst mobile. I have a phone whose battery lasts me 3 days of normal use (web browsing, Twittering, some music, some photos, updating the calendar, email) and I can coax more days out of it with less use.
So on the whole, I'm a happy E71 user, and hope that the phone lasts me a good 18 months or so before the next best thing is released!